A runtime error is a program error that occurs while the program is running. The term is often used in contrast to other types of program errors, such as syntax errors and compile time errors.
There are many different types of runtime errors. One example is a logic error, which produces the wrong output. For example, a miscalculation in the source code or a spreadsheet program may produce the wrong result when a user enters a formula into a cell. Another type of runtime error is a memory leak. This type of error causes a program to continually use up more RAM while the program is running. A memory leak may be due to an infinite loop, not deallocating unused memory, or other reasons.
A program crash is the most noticeable type of runtime error since the program unexpectedly quits while running. Crashes can be caused by memory leaks or other programming errors. Common examples include dividing by zero, referencing missing files, calling invalid functions, or not handling certain input correctly.
NOTE: Runtime errors are commonly called referred to as "bugs," and are often found during the debugging process, before the software is released. When runtime errors are found after a program has been distributed to the public, developers often release patches, or small updates, designed to fix the errors.