Full explanation
LTV is how much money you can expect from a single customer over their full relationship with your product.
It depends on two things: how much they pay each month, and how long they stay. Reducing churn directly increases LTV.
LTV is the number that tells you how much you can safely spend to acquire one customer. If your LTV is 300€, paying 50€ in CAC is great. Paying 250€ is risky.
Concrete example
Your average customer pays 20€ per month and stays 15 months. Your LTV is 300€.