  We present the analysis of the full MaNGA DR17 sample to characterize its
population of compact galaxies. We focus on galaxies that fill the stellar mass
(M$_{\star}$) gap between compact elliptical galaxies (cEs; $8 \lesssim \log
\left(M_{\star} / M_{\odot} \right) \lesssim 10$) and compact massive galaxies
(CMGs; $10 \lesssim \log \left(M_{\star} / M_{\odot} \right)$). We study their
stellar populations and kinematics to reveal how their properties depend on
stellar mass. We select compact galaxies in the MaNGA DR17 sample according to
their effective radius ($R_e$) and stellar mass. 37 galaxies fulfill our
selection criteria in the bridging region between cEs and CMGs. We derive their
kinematics and stellar population parameters from the stacked spectra at
1~$R_e$ using a full spectral fitting routine. We then classify the selected
compact galaxies in three main groups based on their stellar population
properties. One of the groups shows characteristics compatible with relic
galaxies, i.e. galaxies that have remained mostly unchanged since their early
formation epoch ($z \sim 2$). Another group shows more extended and continuous
star formation histories (SFHs). The third group shows a low star-forming rate
at initial times, which increases at around $\sim4$ Gyr. We compare the derived
properties of the selected galaxies with those of previously studied compact
galaxies at different mass ranges. The selected galaxies successfully fill the
mass gap between cEs and CMGs. Their properties are compatible with the
assumption that the scaling relations of compact galaxies at different mass
ranges are related, although galaxies in the first group are clear outliers in
the fundamental plane, suggesting different formation mechanisms for this relic
population.
