Form
Tense
suffix
The kanji and the word share one of the same meanings: form. It doesn't just mean form though, it means tense too. Like verb tense.
けい
This has the same reading as the kanji you learned, meaning you know the reading!
です・ます形ではなしをするとていねいにきこえます。
When you talk using desu and masu forms you sound polite.
ひてい形から会わに入る人はコミュしょうのかのうせいがたかい。
A person who starts conversations with negative form sentences is likely to have some difficulties in communicating with others.
どうして今、過去形で言ったの？
Why did you just say that in past tense?