Introduction to the song (!)
A form part that is repeated several times with the same melody and chord progression, but with different lyrics each time. The verse normally carries the story part of the song. The melody may change slightly to accommodate variations in the number of syllables in the lyrics.
After the verse, the pre-chorus provides a buildup to the chorus. The buildup may be done by having the melody start to rise, increasing the rhythmic and/or harmonic activity, increasing the volume, etc. It may have the same words each time, or there may be different words that provide a connection from the lyrics of the chorus to those of the chorus that follow.
A form part that is repeated several times, with the same melody, chord progression, and lyrics each time. The lyric often sums up the meaning of the song. Often times the "hook" (a particularly catchy part) is contained in the chorus since it has the chance of being repeated many times.
Contrasting material to the verse and chorus, containing new harmonic, melodic, and lyrical material. Often times the bridge moves to a new key and may happen only one time during the song. The bridge rarely contains the hook.
Like the bridge, an interlude provides a contrast to the verses and choruses. Often times it is based on the harmony and texture of the song's introduction, or it may take place over the verse's chord progression, or it could be completely new harmonic material.
The ending may be used to postpone having the song finish. It can use familiar harmonic and lyrical material (for example, repeating the last line) or use something new. A common technique is to continue vamping on a section such as the chorus and fade out.
A "tag" is another word that is applied by some musicians to a certain type of ending. The "tag" is a short phrase that may not have anything to do with the melody or chord progression of the rest of the song. Often time they are musical clichés which can be (and have been!) tagged on to many different pieces, for example:
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Jazz standards often have an "A" section (typically 8 bars) which is then repeated. The "B" section (or "bridge") provides contrast, before returning to a final repetition of the "A" phrase.