"An OLTP database that supports the business operations - for example, logging orders and tracking customers. An operational database is usually the source of data for the data warehouse. Operational data is updated frequently to reflect the current value of all transactions." (Microsoft Corporation, "Microsoft SQL Server 7.0 Data Warehouse Training Kit", 2000)
"A database containing a company's up-to-date and modifiable information." (Glenn J Myatt, "Making Sense of Data: A Practical Guide to Exploratory Data Analysis and Data Mining", 2006)
"A database that is designed primarily to support a company’s day-to-day operations. Also known as a transactional database or production database." (Carlos Coronel et al, "Database Systems: Design, Implementation, and Management" 9th Ed, 2011)
"A database system that runs core functions to the business in production environments. These are not test or reporting database systems, but actual systems that run the operations of the company." (Jason Williamson, Getting a Big Data Job For Dummies, 2015)
"The database of record, consisting of system-specific reference data and event data belonging to a transaction-update system. It may also contain system control data such as indicators, flags and counters. The operational database is the source of data for the data warehouse. It contains detailed data used to run the day-to-day operations of the business. The data continually changes as updates are made, and reflects the current value of the last transaction." (Information Management)
"The database that contains the live data that is viewed, retrieved, and edited in an Oracle Service Cloud application. While reports that are run on the operational database can access real-time data, the reports cannot process as much information as reports that are run on the report database." (Oracle)
"They carry out regular operations of an organisation and are generally very important to a business. They generally use online transaction processing that allows them to enter, collect and retrieve specific information about the company." (Data Floq)