noun, na-adjective
good at conversation; smooth talker; conversationalist
Describes a person who is skilled at talking, often with a nuance of being glib or charming. Can be used positively or slightly negatively depending on context.
彼は口上手だから、初対面の人ともすぐ仲良くなる。
He's a smooth talker, so he quickly becomes friends even with people he's just met.
口上手なセールスマンにうっかり契約させられた。
I was tricked into signing a contract by a glib salesman.
口がうまい is a common phrase meaning 'smooth-tongued' or 'honey-mouthed', often with a negative connotation of being insincere. 口上手 can be more neutral.
Compound of 口 (mouth, speech) and 上手 (skillful). The exact historical derivation is uncertain, but the meaning is transparent from its components.