What is validation?
Validation is a process of testing and ensuring that the user has entered required and properly formatted information through the web form.
What is Client-side validation?
What is Server-side validation?
In server-side validation, all the input validations and error recovery process is carried out on the server side. It can be done using programming languages like C#.NET, VB.NET etc.
Differences and comparison:
Client-side validation is faster than server-side because, the validation takes place on client side (on browser) and the networking time from client to server is saved.
On the other hand, server-side validation is done on the web server. Then the server renders the data into html page and sends back to the client (browser).
Server-side validation is more secure than the client-side as the user cannot see the code even he does a view-source.
Both the validation methods have their own significance. I would like to recommend that you should use both the validation methods Client-side validation to provide a better user experience and server-side to be sure that the input you get from client (browser) is actually validated and not just supposed to be validated by the client.