A post is a main vertical or leaning support in a structure similar to a column or pillar but the term post generally refers to a timber but may be metal or stone. A stud in wooden or metal building construction is similar but lighter duty than a post and a strut may be similar to a stud or act as a brace.
Studs are vertical 2 by 4 inch beams that support the frame of your home. You can find them behind your drywall, usually spaced 16 or 24 inches apart. Since studs are made of thick and sturdy wood or metal, they can securely hold screws better than wall materials like drywall.
A king stud is a vertical structural element that is placed off layout adjacent to a framed opening on each side, such as a door or window. It is the same length as the common studs in the wall and fastened in a similar manner.