### Dropping higher powers of a variable in an expression

Many a times in symbolic manipulations, I end up with lots of terms of higher powers of a variable. Is there a command to drop all the terms above a given power from a symbolic expression?

Eg: from an expression f(x)= x+ x^2 + x^3 + x^4

I want to get only upto 2nd order. i.e. g(x)= x + x^2

I also want to do this on a symbolic matrix.

This will be very useful for simplifying expressions upto lower order terms for further calculations.