The environment variable for the bash prompt is called
PS1 (usually set in ~/.bashrc). What does PS1 stand for? Is there a PS2?
PS1 stands for "Prompt String One" or "Prompt Statement One", the first prompt string (that you see at a command line).
from slightly paraphrased from The Bash Reference Manual
PS1 The primary prompt string. The default value is ‘\s-\v\$ ’.
PS2 The secondary prompt string. ie for continued commands (those taking more than one line). The default value is ‘> ’.
PS3 The value of this variable is used as the prompt for the select command. ie for input into a running script. If this variable is not set, the select command prompts with ‘#? ’.
PS4 The value is the prompt printed before the command line is echoed when the -x option is set. The first character of PS4 is replicated multiple times, as necessary, to indicate multiple levels of indirection. The default is ‘+ ’.
PS1 and PS2 are from the original sh, PS3 and PS4 were added as part of bash
See examples here