What is the sentence 'Jackdaws love my big sphinx of quartz' an example of?

It is a pangram.
A pangram is a sentence that contains all letters of the alphabet.
http://www.rinkworks.com/words/pangrams.shtml

That looks like a pangram to me, a sentence that contains all the letters of the alphabet

http://www.rinkworks.com/words/pangrams.shtml

This is an example of a pangram.

A pangram is a sentence that contains all letters of the alphabet. Less frequently, such sentences are called holalphabetic sentences. Interesting pangrams are generally short ones; constructing a sentence that includes the fewest repeat letters possible is a challenging task. However, pangrams that are slightly longer yet enlightening, humorous, or eccentric are noteworthy in their own right.

By far the most well-known pangram is, "The quick brown fox jumps over a lazy dog." Frequently this is the sentence used to test out new typewriters, presumably because it includes every letter of the alphabet. Curiously, this sentence is often misquoted by changing "jumps" to "jumped." The past tense version, lacking an "s," is not a pangram. Often, too, it is misquoted as "the lazy dog" rather than "a lazy dog." This error is not as grievous; the sentence remains a pangram, just a slightly longer one.

Others include:

Sixty zippers were quickly picked from the woven jute bag

and

Six big juicy steaks sizzled in a pan as five workmen left the quarry.

http://www.rinkworks.com/words/pangrams.shtml

Here are some more from the link - there are many more :-)
The first is the most familiar one from typing classes :-)

The quick brown fox jumps over a lazy dog. (33 letters)
Pack my box with five dozen liquor jugs. (32 letters)
Jackdaws love my big sphinx of quartz. (31 letters)
The five boxing wizards jump quickly. (31 letters)
How quickly daft jumping zebras vex. (30 letters)
Quick zephyrs blow, vexing daft Jim. (29 letters)
Sphinx of black quartz, judge my vow. (29 letters)
Waltz, nymph, for quick jigs vex Bud. (28 letters)
Blowzy night-frumps vex'd Jack Q. (26 letters)
Glum Schwartzkopf vex'd by NJ IQ. (26 letters)
http://www.rinkworks.com/words/pangrams.shtml

Aside from an unusual image, it is an example of a sentence that does not use the letter 'e', unusual in English. It is the most frequently-used letter, comprising roughly 12%, or one-eighth, of letters in the written language.

https://en.wikipedia.org/wiki/Letter_frequencies

.... lov E......

If you please, here is the most famous one in French.
It contains only 37 letters, which is unusual:
"Portez ce vieux whisky au juge blond qui fume"

http://fr.wikipedia.org/wiki/Portez_ce_vieux_whisky_au_juge_blond_qui_fume