What's the meaning of strength?

[rkatcosmos]

I am coming across definitions which says certain substances (like martensite) are hard but brittle. I can't understand the meaning.
Brittle substances have yield strength closer to breaking strength. If something breaks/fails easily then how can it be hard..?
Pls help me out with some numbers...

 

[mfb]

It can be hard to compress the material - you need a large force for a tiny change in its shape/volume/...

 

[462chevelle]

the harder they are the less flex they have and they will break easier to a point. its like mounting something up completely solid. its harder but more likely to break things because it cannot absorb vibration or impact as good. it just takes the force. so a certain force will be lower on something with more flexibility. I think I kind of rambled. but it makes sense to me

 

[SteamKing]

There are several definitions of hardness:
http://en.wikipedia.org/wiki/Hardness