I would have included these in the previous chapter for frequently used expressions / words, but a lot of people seem to get these two mixed up and they needed their own chapter otherwise the previous one would have been too long.
Visuals and Face of the group are too often mixed up.
Visual - The visuals of the group are basically the 'most aesthetically beautiful (or handsome)' members of their respective groups. For the western people, it is a bit taboo to comment on beauty because of the belief that everyone is beautiful in their own right and beauty cannot be measured. However, in countries like Korea, Japan, and China, they have a certain look they favor, that if a person fits that certain look, then he or she is considered beautiful. People are more vocal about beauty standards in Korea; this is why there is this role that is ever present in each kpop group. Visuals also have the most screen time in music videos (and guests in other artists' music videos too), and are the ones their entertainment/company often pushes to do variety shows (as they are known for having the variety skills of the group). They usually become the MCs or guest in shows as themselves outside of their group. They also usually become the first actors/actresses of their group. If you don't know who the visual is or is not really convinced that they are the visuals, they are the ones who get praised on interviews or shows for being very visually attractive. They also get the CFs that are related to beauty and looking good.
Examples: T.O.P (Big Bang), Sulli (f(x)), Nichkhun (2PM), Dara (2NE1), Naeun (APink), Yoona (SNSD), Bora (SISTAR), Mark (Got7), Irene (Red Velvet), and previously it was Luhan for EXO, but now it's Chanyeol and maybe Sehun.
Face of the Group - Faces of the groups are basically called the centers. If you hear idols say 'center', they are the faces of the group. Faces are basically the 'brand name' of their group. They are the centers in pictures and blocking/choreography. Even if they don't really have a solo part, they are still being put in the middle of choreography (even if they aren't part of the dance line). Basically just really a lot of center positions. They share the screen with their group's visual. They are also, usually, the 'favorite' of the company. The company usually throws projects to the face or gives them very noticeable positions in their songs. The company also markets this member a lot and the faces are also often seen as one of the more popular members of their groups. They are usually the first names people say or think of when it comes to mentioning the group that they are in. Because of their marketing, they become one of the more popular members of their groups.
Examples: Kai (EXO), Taeyeon (SNSD), G-Dragon (Big Bang), Jungkook (BTS), Taemin (SHINee), Krystal (f(x)), JB (Got7), Hyorin (SISTAR), Bobby (iKON), Eunji (APink), and Hyuna (4Minute).
There are cases wherein the visual and face are the same person, just like Suzy from Miss A, and Siwon from Super Junior (although people have mentioned that Donghae is the face).
It's also unclear who the visual and face is of SNSD. It's between Yoona and Taeyeon, but a lot of people still argue about who is which. Personally, I think Yoona is the visual and Taeyeon is the face. You're welcome to add your opinions too. (Whether it's SNSD or a different group)