Apparently, the first option (United States Senator (for a six year term) is to finish out Obama's 6 year term that he was elected for back in 2004. The next category (unexpired term) is for a full 6 years after this expired term ends in late 2011. Hope the link explains it better.
Election
If a seat in the US Senate becomes vacant before the end of a term, a replacement Senator is selected according to the law of the particular state involved. Some states use a special election and some have the state governor appoint a Senator to complete the unexpired term.
2004
Senator Dodd of Illinois was elected in 1998. If he decides to run again when his term expires, in what year will the election occur? in 2004
The answer is: B 2004
2004
Lincoln was never a US senator. He served one term -- two years -- in Congress long before he was President. He ran for Senator in 1858, attracted national attention for his debates with Stephen Douglas, but lost the election to Douglas.
A US Senator is elected for 6 years. They are divided into three groups, so that one third are up for election every two years. And only one state senator is up for election at any election cycle (unless there is a mid-term election to replace a senator who has died or resigned).
In the United States Senate, the term in office is six years. After that the senator must either resign or declare that he is running for re-election. There are no limits on how many times a senator can run for re-election.
4 years, with no limits on re-election.
No, he never was. He was a state senator from Illinois for three terms and then a United States Senator for one term.
Illinois State Senators are elected for either a two or a four year term of office with each of the 59 seats staggered to provide a sense of continuity within that body. Thus Senator 'A' might be elected for a two year term for his district, then a four year term followed by a second four year term. That would be a seat with a 2-4-4 rotation. Senator 'B' might be elected for a four year term followed by a second two year term and on the next election he would run for his third term of four years. That rotation would be 4-2-4. Senator 'C' would be in the third rotation of 4-4-2. There are no term limits in Illinois.