I was watching a song video lesson earlier today and it mentioned that the guitar should be tuned to concert pitch. What does that mean? Is it different from the normal EADGBE tuning?
"Concert pitch" comes from how symphonies have learned to deal with tuning various instruments to a common pitch over the years. According to the ISO it's 440 Hertz, which is in the A above middle C range, but, over the years it's been as low as 415, and, even after standardization, is still considered to be in the 430 range in some symphonies. And, according the the linked Wikipedia article, some Baroque ensembles are using A-415 again. So much for standards.
So, it comes from classical music, but for those of us not playing classical it has some useful considerations.
Think in terms of tuning an individual instrument without the aide of a tuner, and then that instrument in relation to another, again without a tuner:
Using an agreed-upon reference pitch AKA "Concert Pitch", such as A-440, lets you tune separately then be in pitch together later. Again, 440 is not a magic number, it's only an agreed-up value and you, and your fellow musicians are free to use something else.
I have several standalone tuners, plus tuners in one amp, and another in my Pod X3, plus one in GarageBand on my Mac. They all allow me to adjust what they should use as their reference pitch, so, once you've shared the reference value it should be no problem for everyone to adjust their particular tuner, so no excuses. :-)
For most of us playing guitar in a band, A-440 is perfectly good. Some bands like to be tuned 1/2 step or a whole step down though. Eddie Van Halen and Stevie Ray Vaughn are two I heard that liked being down 1/2 step. Rather than everyone in the band learn the songs in E-flat or A-flat, they'd tune down and play normally; It's a bit of musical sleight-of-hand that really throws other guitarists off periodically.
Tuning down (or up) can be done either by adjusting the reference frequency, or by leaving it at A-440 then using the tuner's display to track when you're at 1/2 step or 1 step from the reference. Either works, it's really what works for you. It's those less-than-half steps (microtones) that can be a problem and that force adjusting the reference.
Concert pitch basically means that the note A above middle C on a piano (which is the same as A on the 5th fret of the first string of a guitar) shall have a frequency of 440 hertz (Hz). So, tuning to concert pitch means that the entire guitar shall be tuned relative to an A with a frequency of 440 hertz. There are other tunings that utilize different bases for A above middle C (a.k.a. sweetened tunings--see the Peterson Strobostomp page for more information on this) and if you'll notice most tuners like the Strobostomp or the Turbo Tuner allow you to set the base frequency you will be tuning to.