Validator means checking inputed data in any field like 
textBox or dropdownbox any other which we want to validate 
at client side using sever tag.

Following are type of validator control in asp.net.
1. Ranage validator control
2. RequireFieldvalidator control
3. CompareValidator control
4. RegularExpressionValidator control
5. CustomValidator control
6. ValidationSummary control

if we mention in our page but want to disable just use the 
property of validator control causevalidation=false.

In addition of the above answer, it is interesting to know 
the "Turning off Client-side Valiation".

Because validation server contols provide clients with 
client-side validations automatically, you might, at times, 
want a way to control the behavior.

It is quite possible to turn off the client-side 
capabilities of these controls so that they don't 
independently send client-side capabilities to the 
requestor. U can turn off this functionality.

The first is at the control level.  Each of the validation 
server controls has a property called EnableClientScript.  
This property is set to True by default, but setting it to 
False prevents the control from sending out a Javascript 
function for validation on the client.  Instead, the 
validation check is done on the server.