The term 'join up' can refer to a variety of activities, such as mustering, entering, meeting, enlisting, enrolling, signing on, and rendezvousing. Mustering is the process of assembling a group of people for a specific purpose, such as military service. Entering is the act of becoming part of a group or organization. Meeting is the act of coming together in order to discuss or exchange ideas. Enlisting is the process of joining the military or other organization. Enrolling is the process of officially registering with an organization. Signing on is the act of formally agreeing to become part of an organization. Rendezvousing is the act of meeting at a predetermined place and time. All of these activities are related to the term 'join up' and involve joining a group or organization.