Incoming Junior, or incoming Freshman, or incoming Senior means the school year is just beginning. If someone asks "what year are you in?" the incoming Junior would say, "I'm a Junior this year". The college grade levels are:
1st year - Freshman
2nd year - Sophomore
3rd year - Junior
4th year - Senior.
A graduating senior is about to go through the graduation ceremony and receive his college diploma for a Bachelor's of Arts degree (B.A.) If they are going to continue on to a graduate degree, like a Masters (M.A.) or Doctorate (Ph.D.), they will be in graduate school, (college courses above and beyond the B.A. degree).
If a person went to college 1 year, but did not complete a full "college load" or did not complete 30 college credits, they will still be at the Freshman level. They can attend many years, and not finish a full year's amount of college credits or units, so they should not call themselves a "junior".