Data corruption

Data corruption is errors in computer data that happens while the computer is reading, writing, storing, transmitting or processing the data. Such errors introduce unintended changes to the original data. 
If data corruption happens in a file, unexpected results will happen when accessed by the system or an application; such results may range from a minor loss of data to a system crash. For example, if a Microsoft Word file is corrupted, when a person tries to open that file with Microsoft Word, they may get an error message. That means that person will get either a file that cannot be opened or a file with a minor loss of data.
One of the ways this can happen is if a power shortage happens while saving the document, the computer cannot power down properly and the file becomes corrupted. 
Hackers can also corrupt data, be it accidentally or on purpose.