The phrase "negative terminal" refers to the end of a battery or electric device where the negatively charged electrons gather or flow out. Full definition
Thus, you can think of the two positive terminals as being one connection point and the two negative terminals as being one connection point. (mechanics.stackexchange.com)
With the battery connected and engine off, if I connect my multimeter negative cable to one particular spot (the steel air conditioning high pressure tube), it gives an unexpected voltage of about 0.4 volts which disappears when I disconnect the battery negative terminal. (mechanics.stackexchange.com)