Traces, Mark
noun
The kanji and the word are exactly the same. That means they share meanings as well.
あと
Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you: When something leaves traces or marks behind, it's because they were there, but now they're gone, and you've come 後 (あと) they left.
私は、ワイングラスに付いた彼女の唇の跡を指でなぞった。
Her lips left marks on the wine glass and I traced it with my finger.