A sales call is a phone conversation or meeting (often times prearranged) during which a salesperson tries to convince a potential customer to buy a product or service.
A "sales call" is a telephone call made by a salesperson to a potential customer in order to sell a product or service. A sales call can be synonymous with either "warm" or "cold," depending on the level of interest that the potential customer has previously expressed in the product or service being offered.
A "cold call" is a type of sales call made to a potential customer who has not previously expressed any interest in the product or service being offered. For more info on what a cold call is, see "Cold Call" in the glossary.
In summary, a sales call is any call made by a salesperson to a potential customer, while a cold call is a specific type of sales call made to a potential customer who has not previously expressed any interest in the product or service being offered. As a side note, sometimes sales people will even refer to an in-person visit as a sales call.