What is the term that defines how recently a customer purchased items?

The answer is recency. This part of the RFM model. It is a marketing investigation tool used to classify a firm's best customers by calculating definite factors.

The RFM model is founded on three quantitative factors which are:

Recency - How recently a customer has made an acquisition or purchase of productFrequency - How frequent or often a customer makes a purchaseMonetary Value - How much cash a customer spends on purchases

RFM analysis often sustains the marketing saying that "80% of business comes from 20% of the customers."