What does the 17P mean in the name of the Holmes Comet?

Question

The 17P Holmes Comet is in the sky now in Perseus. I want to find out why it is named 17P Holmes. It is in the northeast sky.

Answer 1

Because the names of discoverers don't allow for a unique identification, comets receive a more official name.

The initial name consists of a one-letter prefix (C for "comet" or P for "periodic comet") followed by the year of discovery and an uppercase letter that indicates the half-month in which the discovery occurred.
For example, an A represents January 1 though 15, B is January 16 through 31, and so on. (The letter I isn't used to avoid confusion with earlier nomenclature that used Roman numerals, and the letter Z isn't necessary.)
After this letter comes a number that represents the order of discovery during the half-month.
For example, Halley's Comet, which was the first comet discovered or recovered in the second half of October 1982, therefore receives the designation P/1982U1.
When the return of a comet is well established, astronomers add a number to the prefix (then next number available in the list maintained by the IAU).
Since Halley was the first comet whose return was identified, its full designation becomes 1P/1982U1.

Significant comets also have the discoverer's name added, and the year/month designation is usually dropped in common usage.

So 17P/Holmes was the 17th confirmed periodic comet.

Answer 2

Holmes is of course the discoverer. The P indicates a periodic comet - one that comes back around the sun every few years. 17 indicates it was the 17th such comet discovered.