What is the difference between certificates used on the client side and certificates intended for the server?

Certificates for the server and client differ in purpose and content:

• Server certificate is used to verify the authenticity of the server to the client. It contains the server's public key and information that allows the client to verify that it is indeed communicating with the correct server (e.g., domain name).

• Client certificate is used for client authentication to the server. It contains the client's public key and allows the server to verify the client's identity.

Main differences:

1. Purpose: server certificate confirms the server, client certificate — the client.
2. Usage: server certificate is usually required for HTTPS, client certificate — for mutual TLS authentication.
3. Content: the certificate specifies the subject — for the server, it is the domain name; for the client, it is the username or device.

Thus, certificates differ in their role in establishing a secure connection.