The heater core is leaking.
Hello! That is a common problem with your particular vehicle. The heater core is made of a brass and aluminum material which is known to crack under the "heat stress" it endures. Luckily heater cores are rather inexpensive to purchase and to install. I suggest having the heater core verified to be leaking by a technician to make sure it is not a nearby hose causing the leak.
I want to make sure it is fixed right the first time that is why I suggest a leak verification. I would recommend having a certified mechanic, such as one from YourMechanic, come and fix your leaking heater core for you.