a pattern of marks
"The tiger's coat features distinctive black markings that help it blend into the shadows."
the act of making a visible mark on a surface
"The child spent hours marking the whiteboard with colorful markers to create his favorite cartoon characters."
The action of marking.
"The teacher spent the morning grading papers, which involved carefully putting a red mark next to every spelling mistake."
present participle of mark
"The student is marking her important notes in a different color pen to ensure she remembers them later."
In plain English: To mark something means to put a sign, symbol, or note on it so you can find it later or show that someone has done their work.
"The teacher is marking all the students' essays today."
The word comes from the Old English term for "making a mark" and entered modern usage through Middle English with that same meaning. It is formed by combining the root word mark with the suffix -ing.