Hey Dhiraj
You might want to consider using either custom tags or labels instead for what you're after. Tags are really designed to be added by anybody, if they have the permission to do so. The list that you're seeing is probably comprised of tags that other contributors have added to posts themselves rather than by an administrator. Custom tags and labels both give administrators a lot more control over which words/terms are used and labels can also be made mandatory and be predefined at the board level.
Take a look at our TKB articles and if you have any further questions please get back to me.
Regards
Noaman
