What term refers to a long speech made by a single performer or character?

The term that refers to a long speech made by a single performer or character is a monologue. In theatrical contexts, a monologue is an extended speech delivered by one character, allowing them to express their thoughts, feelings, or important information directly to the audience or to other characters. This can provide insight into the character's mind and motivations.

Monologues are pivotal in drama, as they can serve to develop the character further, set the scene, or convey critical plot points without interruption from other characters, which distinguishes them from dialogue, where two or more characters engage in conversation. Additionally, while a soliloquy—a type of monologue spoken by a character alone on stage—specifically reveals a character's internal thoughts and does not address other characters, a monologue can be performed in front of others and directed to them as well.

A conversation implies an exchange between multiple characters, which does not apply here, making monologue the most accurate choice for a lengthy solo speech in performance.