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In the context of databases, a transaction is a unit of work performed within a database management system against a database, and treated in a coherent and reliable way independent of other transactions. A transaction generally represents any change in a database.

Non-Relational Database, often referred to as NoSQL databases, are databases that do not follow the relational model provided by traditional relational databases. They can store structured, semi-structured, or unstructured data and are optimized for performance, scalability, and flexibility.

Sharding is a type of database partitioning that separates very large databases into smaller, faster, more manageable pieces called 'shards'. Each shard is a discrete database that forms part of a larger database system. Sharding is used to scale databases that can no longer handle their workload as a single, unified system.

A data lake is a system or repository of data stored in its natural/raw format, usually object blobs or files. A data lake is usually a single store of all enterprise data including raw copies of source system data and transformed data used for tasks such as reporting, visualization, analytics and machine learning.

ACID stands for Atomicity, Consistency, Isolation, Durability. These properties ensure reliable processing of database transactions. Atomicity ensures all parts of a transaction are treated as a single operation; Consistency ensures the database remains in a valid state; Isolation ensures concurrent transactions do not interfere with each other; Durability ensures completed transactions are saved permanently even in the event of a failure.

A Foreign Key is a set of one or more columns in a database table that refers to the primary key in another table. Foreign keys establish a relationship between the data in two tables and are used to ensure referential integrity of the data. They also prevent certain actions that would destroy links between tables.

A Primary Key is a special relational database table column (or combination of columns) designated to uniquely identify all table records. It must contain unique values and it cannot contain NULL values. A table can have only one primary key, which may consist of single or multiple fields.

A relational database is a type of database that stores and provides access to data points that are related to one another. Relational databases are based on the relational model, which organizes data into one or more tables of columns and rows, with a unique key for each row.

In databases, a join is an SQL operation used to combine records from two or more tables in a database. A join is performed based on a related column between them. Common types of joins include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN.

A database schema is the skeleton structure that represents the logical view of the entire database. It defines how the data is organized and how the relations among them are associated. It formulates all the constraints that are to be applied to the data.

Normalization is a process in database design that organizes data attributes (columns), so they're correctly partitioned to reduce redundancy and improve data integrity. It involves creating tables and establishing relationships between those tables according to rules designed to protect the data and make the database more flexible by eliminating redundancy and inconsistent dependency.

The CAP Theorem, also known as Brewer's Theorem, states that a distributed computer system cannot simultaneously guarantee Consistency, Availability, and Partition tolerance (CAP). According to the theorem, a distributed system can only provide two of the three guarantees at the same time, not all three.

A database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database. Common uses of triggers are auditing changes, enforcing business rules, maintaining complex integrity constraints, and cascading deletes or updates.

An index in database systems is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space. Indexes are used to quickly locate data without having to search every row in a database table every time a database table is accessed.

Concurrency control is a database management systems technique to ensure that multiple transactions occur concurrently without violating the inconsistency of the database. It prevents transactions from interfering with one another while ensuring that database operations are performed in a safe and consistent manner.

Data mining is the process of discovering patterns and knowledge from large amounts of data. The data is often voluminous, but as it is mined, valuable information can be discovered. Data mining involves the use of sophisticated data analysis tools to discover previously unknown, valid patterns and relationships in large data sets.

Data Warehousing is a system used for reporting and data analysis, considered a core component of business intelligence. DWs store current and historical data and are used for creating trending reports for senior management reporting such as annual and quarterly comparisons.

Object-Relational Mapping (ORM) is a programming technique for converting data between incompatible type systems using object-oriented programming languages. It creates a 'virtual object database' that can be used from within the programming language. It aims to bridge the gap between how data is represented in objects vs. relational databases.

The Entity-Relationship Model is a conceptual tool for data modeling which allows the representation of entities, attributes, and relationships. It is a high-level diagrammatic representation used to design applications and systems at the conceptual level, often as the first step in database design.