Total Advance: This is the sum of ignition advance in crankshaft degrees from all sources. Most V-8s operate best with between 30-36 degrees of total advance, so if the initial timing is set for 8 degrees BTDC, and the mechanical advance adds another 24 degrees; you'd have 32 degrees total advance, also referred to as total timing. Note that vacuum advance does not figure into total advance, since there is no vacuum at wide-open throttle.
Advance Rate: This is how "quickly" the additional advance is applied, usually expressed in terms of rpm, including the point where advance begins and the point where timing is "all in." The ideal rate depends on a number of factors, including transmission type and ratios, rear-axle ratio, and vehicle weight. Most drag racers like to get the advance in quickly to make maximum power, but many stock passenger vehicles can't apply maximum advance as quickly without triggering detonation. Most vehicles begin to advance just after 1,000 rpm; performance-tuned drag cars may have all the timing in shortly after 2,000 rpm, while stock smog-era cars may not realize total advance until nearly 4,000 rpm. Determining the precise rate and amount requires testing and tuning for individual applications, and razor-sharp race tunes may even vary with fuel quality and weather and ambient temperature conditions.
Advance Curve: All the factors that make up the ignition timing for a particular application-initial, mechanical, vacuum, total timing, the advance rate, and so on, work together to make up the advance curve. The curve refers to the performance characteristics of a particular vehicle's ignition timing advance system.
Crankshaft Degrees vs. Distributor Degrees: Ignition timing is usually expressed in terms of crankshaft degrees, since the relationship that is being tuned is between the spark timing and the position of the crank. However, a potentially confusing aspect of ignition tuning is that advance curves are often described in terms of distributor degrees. When using distributor degrees, simply multiply by 2 to get crank degrees, since the distributor rotates at half the speed of the crank when installed in the engine.