It is slang and Japanese English which is derived from “through”. It is a noun which means “to ignore”. It is used to describe situations in which you intentionally give no attention to someone/something. “スルーする“ is the verb.
“しかとする“ is a synonym for “スルーする”. These two are slang of "無視する".
“(既読)スルーする“ is often used when you read a message without replying. “(既読)スルーされる“ is also used when the message you sent is marked “read”, but they haven’t responded.
- Meg: 風邪を引いたかも。今夜は少ししか飲まないし、早めに帰るね。
I might have caught a cold. So I’m going to drink very little tonight and go home early. - Amy: 私も。長時間(上司とは)一緒にいられないよ。くだらないダジャレを言うし、酔うと説教しだす(orし始める)からさー。
Me too. I can't stand being with him for a long time. He always makes bad puns and starts to lecture after he gets drunk. - Meg: わかる。悪い人じゃないけど、(冗談が)つまらないよね。スルーした方がいいよ。
I know how you feel. He is not a bad person, but his jokes are so boring. It might be wise to not pay attention to what he says!
- Meg: はー、イライラする。彼と連絡が取れない!メッセージ送ったのに、既読スルーされた!
I’m so stressed out. I can’t get a hold of him! I texted him and the message was marked as read, but there’s no reply! - Amy:彼に連絡してから、どれくらい経つの?
How long has it been since you contacted him? - Meg: 三日くらい。まだ、スルーして(い)る。
Almost three days. He is still ignoring me.