CAC refers to Customer Acquisition Cost and CLTV refers to Customer Life-Time Value. CAC is the money you spend to acquire a new customer. CLTV is the money that you can expect to make from a customer throughout their lifetime as a paying customer. You cannot calculate your CAC in isolation. Your CAC has to be calculated with regards to CLTV because CAC does not include customer retention cost. And customer retention is an incredibly important part of increasing CLTV. Therefore these two metrics have to be balanced against each other.