Learn English – What term is used for the programs that are educational and entertaining

Your question is somewhat misleading, and may contain a false assumption. A statement like the following:

Customers who have never paid a dime

is not a sentence. It's a noun phrase. Let's break that down:

Customers is a noun. Nouns are not inherently subjects or objects, so it's not correct to refer to this as either the subject or the object.

The remaining part who have never paid a dime is a relative clause, which is an embedded sentence that is used to modify something in the larger context. The subject of the embedded clause is the relative pronoun who, and the remainder have never paid a dime is the predicate of the relative clause.

However, using terms such as "predicate" and "relative clause" may be intimidating to people using your software. My best offering for newbie-friendly terminology would be:

• Call Customers a noun (most people at least know what that means)
• Call who a "question word", and make it clear by example what you're referring to
• Call have never paid a dime a "description"

There are several networking terms that can apply here.

• Poor quality indicates that there is an issue with the recording or playback of the audio. It can refer to the quality of the microphone, the ambient noise in the microphone's location, the processing capability of the computer to which the microphone is connected, the microphone's attempt to alleviate feedback, the quality of the speakers at the receiving end, or the processing capability of the computer receiving the audio.
• Lag generally refers to the delay between transmission of the sound and reception of it. If the other person is listening to you through a set of speakers, you will sometimes hear an "echo" when your voice is played through the other's speakers.
• Latency refers to the ability of the network to continuously stream the audio. This sounds like the other person is "breaking up" because the network is losing pieces of the audio stream.