1A shortened form of a longer word or phrase (an abbreviation); also the omission of part of a text. Extremely common in the pattern 「Xは Yの略」(X is short for Y).
「スマホ」は「スマートフォン」の略だ。
「Sumaho」 is short for 「smartphone」.
「国連」は「国際連合」の略です。
「Kokuren」 is the abbreviation for 「United Nations」.
参考文献は紙面の都合上、略とした。
The references were omitted due to space constraints.
議事録では重要でない部分に（略）と書かれていた。
In the minutes, unimportant parts were marked with 「(omitted)」.
2A rough outline or the gist. In modern Japanese this normally appears in compounds like 概略 or 大略; used alone it sounds somewhat literary.
詳細は省くが、事の略はおおよそこうである。
I'll leave out the details, but the gist of the matter is roughly this.
彼はその計画の略を手短に語った。
He briefly described the outline of the plan.
3A plan, scheme, or strategy. In modern Japanese it appears in compounds such as 策略 (ploy), 知略 (resourcefulness), or 計略 (stratagem); standing alone it is archaic and literary.
敵の略にまんまとはまってしまった。
We fell right into the enemy's scheme.
彼の略は巧みで、誰も見抜けなかった。
His scheme was so skillful that no one saw through it.