look up any word, like sex:
 
2.
when you can't get off the couch.
"Man, Jessica had so much inertia the other day, she couldn't even get off the couch!"
by smoking-glove December 20, 2012
 
1.
Simple terms: The 'reason' that to why you have to use some sort of effort to move or stop something like an object.

The law/principle of inertia states that a body at rest will remain at rest and a body in motion will continue moving with a constant velocity unless acted upon by an external non zero force.

Don't confuse this with momentum
Due to inertia, a moving body in space (ie a vacuum) will not stop or deviate unless another non zero force acts on it (eg gravity)
by White Razor March 25, 2007
 
3.
Tendency for a person to resist a change in movement; Force needed to generate the momentum to cause movement
"I'm hungry, but have no inertia to get up and go eat"
by Supersuperdude August 31, 2011
 
4.
Boostbuddy line of performance and making your slow car fast
I bought my turbo from Inertia and it's boosts like crazy!!!
by yourfriendlyasshole May 17, 2006