In 2016, “cisgender” entered into the dictionaries as an adjective used to describe an individual whose gender aligned with their sex. You may also see the term “cis” in reference to a non-trans person. It is a descriptor, much like “trans” or “transgender” might be used to describe someone.
Masculinity generally refers to the characteristics that society has assigned to men. Although masculinity is often assigned to men, it is largely a social construct that outlines physical characteristics, mannerisms, and personality.
For the individualistic piece, masculinity is partially embedded in instinctual behaviours and partially based on social settings. In the animal kingdom, males are often in a protective and hunting role even though these roles are certainly not exclusive to males.
Most people will have characteristics that are considered masculine, regardless of sex or gender. This is the same for femininity and feminine traits.
A transgender individual is someone who was born a certain sex and assigned the correlated gender to the sex observed, but do not align with their physical sex and assigned gender. For example, a transgender woman is someone who was assigned male at birth but now presents and lives as a woman.