Mean (/mi:n/) is an English verb meaning "to intend" or "to convey a meaning". It is an important language-related verb.
Mean is an irregular verb - the third person form is "means" (/mi:nz/), the -ing form "meaning" (/mi:nɪŋ(g)/), and it has an irregular preterite and past participle "meant" (/ment/).
"What do you mean?" is a common way of asking for clarification. "I see/know what you mean" is good for back-channelling to indicate understanding.
Note the multi-word verb form "meant to".