A variable's change in math or science, clear, discrete A river mouth that opens wide, and yawning meets the sea A triangle when capital, if viewed linguistically

The bigger I am, the more I hide, In salty water I glide. Penguins watch me pass, I'm a giant's looking glass. What am I?

its a color... a type of music... a mood... half the color of the big globe we're on.

A visit to me at the park, a visit to me at a few designated schools, workplaces if the boss is cool, beachside at a lax time as a breezy tool. You laugh, you lay, you play, you sit, you eat with me.

Flat land as far as the eye can see; the opposite of fancy; the American midwest