Concurrency may refer to any of the following:
1. The performance of multiple calculations at the same time on a computer system. The calculations can be separated by using two separate processors, one processor with additional cores, or by using different threads on the processor. The calculations may or may not interact with one another at some point in the process.
Computer programmers can take advantage of this when creating applications, and more information on using this with programming can be found at Concurrency Programming Guide: Introduction.
2. When working with databases, concurrency controls are used to make sure each transaction on the database takes place in a particular order rather than at the same time. This keeps the transactions from working at the same time, which could cause data to become incorrect or corrupt the database.
For instance, if two transactions are attempting to write data into the same column or row of a database table and they write to it at the same time, one or both entries could be lost. Concurrency controls ensure that each transaction is processed one after the other, so that the data is entered properly.