Peering refers to:
a. high-speed data lines provided by many firms all across the world that interconnect and collectively form the core of the internet.
b. the broadband service provided via light-transmitting fiber-optic cables.
c. the language used to compose web pages.
d. a situation when separate isps connect their networking equipment together to share traffic.
e. a system that connects end users to the internet.

Peering refers to a situation when separate ISPs connect their networking equipment together to share traffic.

Explanation:

In computer networking, peering is a voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the users of each network.

It allows ISPs to directly hand off traffic between each other's customers, without having to pay a third party to carry that traffic across the Internet for them.