Hypomasculinity is a sociological and psychological term for the absence of stereotypical male traits. For example, it is the absence of the de-emphasising of feelings and relationships. Oftentimes, individuals who exhibit hypomasculine traits display unmasculine professional or physical characteristics that deviate from the norm.
A Jungian interpretation of this would be of an overwhelmingly strong anima or female complex. This term can be pejorative and it is important not to place a moral interpretation on whether it is desirable, only by whether it is adaptive or maladaptive. Its opposite behavior is termed hypermasculinity.
Hypomasculinity can be understood in relation to a broader gender construct presented by R. W. Connell and James Messerschmidt https://etnologia.uw.edu.pl/sites/default/files/hegemonic_masculinity_connell_and_messerschmidt.pdf . Within their theoretical framework for masculinity studies, hegemonic masculinity represents the culturally dominant idea of "manhood". Other ideas like subordinated, marginalized, hypomasculinity, or non-hegemonic masculinities are described in contrast to it. These non-hegemonic categories are described with similar traits or behaviors that do not conform to dominant masculine norms (hegenomic masculinity). Masculinities are explained to be socially constructed and context dependent https://etnologia.uw.edu.pl/sites/default/files/hegemonic_masculinity_connell_and_messerschmidt.pdf, meaning hypomasculinity varies across culture, society, and historical settings. Hypomasculinity is defined by social experiences that are labeled as "less masculine".