A growth tank was a form of tank in which a lifeform such as a clone was artificially grown.
In 2153, a growth tank in sickbay of Enterprise NX-01 was temporarily used to hold a Lyssarian Desert Larvae that had previously been in another tank and was intended to be grown into a mimetic simbiot. Doctor Phlox briefly removed the larva from the growth tank in order to inject it with a hypospray containing blood that had been extracted from a comatose Charles Tucker III. Two days later, the growth tank had been discarded and the simbiot was instead now in a birthing tank. (ENT: "Similitude")
The term "growth tank" comes from the final draft script of "Similitude", in which it was referred to as "a LARGE GROWTH TANK".