A: There are two common scale lengths in use for electric guitars today: 24-3/4″ (used by Gibson for Les Pauls and other guitars) and 25-1/2″ (used by Fender for Strats and Teles and other guitars). There are also other scale lengths in use (such as the 25″ one used by PRS for most of their guitars).
Physically, longer scale length results in tighter feelings strings (all other things being equal). This is because the longer a string is, the more tension is required to bring it to a given pitch.
Tonewise, many guitarists feel longer scale length produces a crisper, brighter tone, while shorter scale length produces a thicker, beefier tone. Of course, this is subjective, and varies from guitar to guitar depending on myriad other factors.