SSL Certificate is the common legacy name for a TLS certificate, which helps authenticate a server as part of a connection that protects data in transit.
It matters because development decisions affect speed, security, scalability, tracking, SEO, and maintenance. A site that looks good but is fragile or hard to update can quietly hold back every marketing channel.
Example
A visitor connects to a checkout page over HTTPS. The site’s TLS certificate, often called an SSL certificate, helps authenticate the server as part of the encrypted connection; it does not prove that the seller is trustworthy.