What is the difference between Query Params and Path Variables?

Query Params or Query Parameters are used for sorting or filtering the resources. On the other hand, Path Variables are used for identifying specific resources.
Path params are part of the url where as query parameters are added after the ? mark symbol and separated from other query parameters by & symbol.

PathParam example
GET http://base-url/students/{roll-number}

QueryParam example
GET http://base-url/students?grade=10