(The information across this website is written primarily for leaders of dependent groups.)
A dependent group is simply one where the participants have a level of dependence upon the leader(s).
An experienced group of bush walkers from the Blue Mountains pay a guiding company to take them hiking in the Snowy Mountains because they do not have the skills/knowledge/experience for hiking in Alpine areas. Whilst they have a high level of competence, they are still dependent on the leader from the commercial company in this context.
The nature of the relationship between the leader and the participants does not have to be one where a commercial transaction has taken place. It also includes volunteers (eg Scouts and Girl Guides), clubs (e.g. bush walking and climbing clubs, public and university clubs) and even someone facilitating an activity for their friends.
It could be under the banner of education, recreation, tourism, therapy, or more.
N.B. there is complexity when groups are inter-dependent or co-dependent (e.g. on a canyon trip: "I know how to navigate and do first aid, but you know how to abseil and do rope rescue")