There are some key elements here:

1. Acting with the knowledge that there will be very undesirable consequences: "This will really hurt." I'm not referring to cases where someone acts in ignorance or in hopefulness that somehow they'll escape consequence.

2. Acting when not doing so carries no consequence. There is no doubt a firefighter is brave for running in a burning house to save a baby, but what of a neighbor? No one will fault the neighbor for not doing so, and I consider it a different kind of courage when risk avoidance is clearly acceptable.

3. Acting without expectation of reward. People often do things expecting reward money or publicity, but sometimes there's no expectation of any reward: they expect no more reward than the knowledge that they did the right thing. The motivation is internal rather than external.

There are a lot of different situations, but choosing to act in the face of likely consequence with no expectation of compensation is my starting point.

PS. I realize #3 isn't about courage but it is something I consider significant.