  The third release of the Gaia catalogue contains the radial velocities for
33,812,183 stars having effective temperatures ranging from 3100 K to 14,500 K.
The measurements are based on the comparison of the observed RVS spectrum
(wavelength coverage: 846--870 nm, median resolving power: 11,500) to synthetic
data broadened to the adequate Along-Scan Line Spread Function. The additional
line-broadening, fitted as it would only be due to axial rotation, is also
produced by the pipeline and is available in the catalogue (field name
gaia_source:vbroad). To describe the properties of the line-broadening
information extracted from the RVS and published in the catalogue, as well as
to analyse the limitations imposed by the adopted method, wavelength range, and
instrument. We use simulations to express the link existing between the line
broadening measurement provided in Gaia Data Release 3 and Vsin(i). We then
compare the observed values to the measurements published by various catalogues
and surveys (GALAH, APOGEE, LAMOST, ...). While we recommend being cautious in
the interpretation of the vbroad measurement, we also find a reasonable global
agreement between the Gaia Data Release 3 line broadening values and those
found in the other catalogues. We discuss and establish the validity domain of
the published vbroad values. The estimate tends to be overestimated at the
lower vsini end, and at $T_\mathrm{eff}>7500\,\mathrm{K}$ its quality and
significance degrade rapidly when $G_\mathrm{RVS}>10$. Despite all the known
and reported limitations, the Gaia Data Release 3 line broadening catalogue
contains the measurements obtained for 3,524,677 stars with $T_\mathrm{eff}$\
ranging from 3500 to 14,500 K, and $G_\mathrm{RVS}<12$. It gathers the largest
stellar sample ever considered for the purpose, and allows a first mapping of
the \Gaia\ line broadening parameter across the HR diagram.
