Concept:
In glass chemistry, oxides are classified as network formers, network modifiers, and intermediates.
Step 1: Network formers are oxides that can form the basic glass network.
Step 2: Common network formers include:
\[
SiO_2,\ B_2O_3,\ P_2O_5
\]
Step 3: \(B_2O_3\) forms borate glass networks and is an important constituent in borosilicate glass.
Step 4: Therefore:
\[
B_2O_3=\text{Network former}
\]
Hence, the correct answer is:
\[
\boxed{\text{Network former}}
\]