Young people change words to fit in their life. Here are some examples in 2018:
つらみ is from つらい. You can change an adjective to a noun if you change い into み. For example, かなしい（sad）becomes かなしみ（sadness）.
So, つらい（mentally painful）became つらみ（mental pain）.
つらい usually becomes つらさ if you want to make a noun from an adjective. さ is another suffix to make an adjective a noun.
フッ is from フットワーク which is ‘footwork’. 軽 is from 軽い（かるい）which means ‘light’. So, what does ‘light footwork’ mean? フッ軽 can be used to describe a person who joins a party asap without hesitation if invited.
It is a short word from スクールバッグ, which means ‘school bag’.