Colloquial means belonging to ordinary informal speech. A colloquial expression, colloquial usage, colloquial and relaxed.
It is a plain description rather than a criticism, since colloquial language is right for conversation and wrong for a contract. It is not the same as slang, which is narrower and belongs to a group.
1adjectivecolloquialBelonging to ordinary informal speech.
“Gonna is colloquial and fine in texts, but don't use it in your essay.”
colloquial is a quality.
Latin colloquium means a conversation, from com plus loqui, to speak.
Latin
colloquium — conference, conversation
English, today
colloquial
Built from
From colloquy + -al. 1751, from earlier term colloquy (“a conversation”), from Latin colloquium (“conference, conversation”), from con- (“together”) + loquor (“to speak”), + -al.
Etymology from Wiktionary, CC BY-SA