'Overdrive' is essentially everything from sound of an amp being slightly pushed to break up to the crunch and distorted warmth of a cranked tube amp.
'Distortion' is usually everything including, and above and beyond that ceiling of the typical gain that on 'Overdrive' pedal has.
All of my gain or boost pedal on my pedalboard would fall under the 'Overdrive' definition of light to medium gain with natural and traditional amp qualities.
The reason I employ Overdrive instead of Distortion pedals in my setup has a lot to do with the style of music that I tend to play, the dynamic response of Overdrive pedals, the option of stacking multiple gain pedals, and the clarity and more articulate tone response.
Let me unpack these four reasons:
Style - If your not playing heavy metal, grunge, thrash or a style that needs over-the-top gain and sustain, distortion pedals can sound thin, buzzy and less articulate than overdrives. I play mostly rock and pop live shows and session and find that my guitar will cut through the mixes better if I use less gain on the pedals and try to highlight the natural and transparent sounds of a tube amp at that slightly broken up setting. I can achieve high gain sounds if I need them by combining two overdrives together.
Dynamic Response - With an overdrive pedal I can clean up my sound by softer picking or using the guitar's volume control. I find that I can use a lot more dynamic control with overdrives that help with building with a songs dynamic range. Distortion pedals tend to give you too much gain to dial up or down dynamically and tend to compress the overall sound.
Stacking - I stack my overdrives all the time in order to use the distinct and special tone qualities of a couple of pedals in combination to achieve new sounds. I might use a mid-range heavy overdrive with a full range overdrive to a cut through a mix for soloing. I might use the gain of one overdrive to push another overdrive over-the-top to get a 'fuzzface' type of sound.
Clarity - Even though it's a lot less forgiving, I tend to turn down the gain of my pedals for the sake of clarity and articulation. A lot of the great guitar albums of the past have had this same mindset and approach to recording and tone, and I the results are generally a more punchy, defined, and distinct sound quality in both live and studio situations.
Try some A/B comparisons at a local store and find out what fits your playing best.
