Maknae 막내 (say: mag-neh) is the youngest person in a group.
Due to the unnie/hyung/dongsaeng dynamic in Korean culture, everyone is expected to take care of people younger than themselves and to give help and guidance when needed. Since everyone in the group is older than the maknae, the members have a certain amount of social authority over the maknae. The maknae is expected to be somewhat obedient to the hyungs or unnies and “listen well 잘 들어.”
All dongsaengs are expected to defer to their elders in most small things and are expected to do things like fetch an item from another room or clear the dishes after a meal, so for the maknae this often becomes a particularly burdensome frustration since they only have elders to please and no dongsaengs to pass tasks to.
The members are usually protective of the maknae. Maknaes are often cuddled, coddled, and doted on by their members.
The maknae is expected to be cute and give lots of aegyo. It’s usually the maknae’s responsibility to give comfort and emotional support to the older members and try to lift the group’s spirits when needed.
When an idol introduces her/himself as the maknae, they are telling you a lot about their place in the group dynamic. They are also usually telling you that they are in charge of cuteness for their group.