These numbers are an abbreviated way of communicating how many skills you have earned in a particular profession.
Every profession has four columns of skills (between novice and master) that a player can learn. Each column in each profession has four boxes, making sixteen skills between novice and master.
A medic 1-0-0-1 has only learned two of the skillboxes above novice, namely the first skill of the first column and the first skill of the fourth column.
A bounty hunter 2-3-3-5 doesn't exist, because there are only four boxes per column (so he can't have 5 in the last column).