Full definition
Vendor is defined as: A vendor is an external party that sells a product or service - often used specifically for technology and SaaS providers, though the term overlaps heavily with supplier.
In IT and procurement teams vendor usually implies a product-led relationship: a software licence, a hardware fleet, a hosted platform. The evidence expected from a vendor leans toward security certifications and data-processing terms.
Because vendor and supplier are used interchangeably in many businesses, the practical answer is to define the term in your own policy and stick to it consistently across your document library.