The term coding refers to codes used to shorten words before we enter them into a database.
In some cases the coding involves  abbreviation (shortening of words) used in the database. Example, we could write 1M instead of writing 1 mile, or C  instead of writing clothes shop. The codes used do not have to be abbreviations. See the example below.
 
 

Using database coding has a number of advantages :-

1) It reduces the possibility of spelling mistakes and typing errors.
2) It makes it quicker to type in data.
3) Databases which make extensive use of coding take up less space on computer disks.
4) Coding can act as a security measure. If confidential database files are stolen they will be useless if the thief does not understand the codes.

Problems with coding occur if:-

1) Users forget what the codes mean. (codes need to be explained in user documentation / instructions)
2) Different database users enter information using slightly different codes.