Tim is the nickname given to listeners of Hello Internet. The name was originally coined by Grey in "H.I. #7: Sorry Language Teachers" at 50:58, referring to the fact that there could be a listener called Tim listening to the episode in an airplane.
Grey elaborates further in "H.I. #65: Operation Zeus" at 26:37 while joking about sending an email to Tim Cook about the sales figures for the smaller iPhone stating:
"Everybody who listens to the podcast is named Tim; and then also, everyone who is named Tim (by definition) also listens to the podcast."