以上【いじょう】

以上 after a number means "or more", "and over". The number itself is included: じゅっこ１０個いじょう以上 is ten or more, not "more than ten". It goes straight after the number and counter, and takes の before another noun.

以上, 以下 and 未満

いか以下 is the downward partner of 以上, and it also includes the number. "Under", leaving the number out, is みまん未満.

So at exactly 18 you are inside 以上 and outside 未満.

"That is all"

At the end of a list, a report or an announcement, 以上 on its own means "that is all". いじょう以上で + a verb of ending closes a talk.

Usage notes

These go beyond a number.

More than expected

After a word like そうぞう想像, よそう予想 or それ, 以上 means "beyond" that point. With に it describes how much; that use is its own grammar point, 以上に.

After a verb

After a plain verb, 以上 means "now that", "since". That use is its own grammar point, 以上は.