A digital certificate plays a crucial role in web security by authenticating the identity of entities and ensuring secure communication over networks. It is issued by a trusted Certificate Authority (CA) and contains the public key of the certificate holder, alongside information about the issuer. Digital certificates employ cryptographic protocols to encrypt data transmitted over the internet, making it more challenging for unauthorized parties to intercept or alter the information. By establishing trust between parties, digital certificates facilitate secure transactions and communications, protecting sensitive information such as passwords and credit card details.