There are two common meanings for the word "contrast".
One type of contrast just refers to the difference between the darkest and lightest parts of the scene - the more the difference, the higher the contrast.
A slight refinement of that description refers only to those parts of the scene where important detail lies - i.e. detailed shadows and detailed highlights.
Some might refer to this as macro contrast. Others would refer to this as something akin to dynamic range.
The other type of contrast refers to the difference between adjacent tones of dark and light in the details of the scene. The greater the difference, the more contrasty those details appear.
Many would refer to this as local contrast or micro contrast.
The quality of light determines the local contrast in the scene.
What follows assumes you are using black and white negative film.
When I am making decisions about exposure and development:
1) the macro contrast is quite determinative of exposure, in that I need to be sure that there is enough exposure for the shadows, but would prefer that the highlights not be over-exposed too much. Usually, the films I use can handle a lot of that though, so it isn't unusual for me to rely on manipulations in the printing darkroom to deal with that. In relatively less common circumstances, the macro contrast of the scene is very small, so I have to depend on the print darkroom to brighten the highlights;
2) the micro contrast influences my development choices, because development controls vary the slope or gamma of the exposure and density response. Increasing development has a similar effect as increasing the contrast or "hardness" of the light on the scene. That development increase may also be used to increase the macro contrast, in situations where the dynamic range in the scene warrants it.