What does "zero drop" mean?
Basically a "zero drop" shoe means that the sole design places your heel at the same elevation off the ground as the ball of your foot.
Most running footwear are designed with a higher heel, generally around 10-16mm, the theory behind this is to provide extra cushioning for the heel and to also tilt the runner slightly forward, supposedly improving running posture and some forward momentum. There are many debates about the effectiveness of this, however it's still the most common design seen today.
The zero drop theory came about due to wanting to provide footwear with a more natural feel, more like you would feel running barefoot, but with protection for the soles of your feet. This is a popular choice for trail runners as speed is not always paramount, but endurance is, and a zero drop can assist in taking away some of the strain from the knees, lower back, etc. and placing this on the calf muscles which act as somewhat of a shock absorber, also lessening the tendency to heel strike as is common with heel to toe drop footwear.
Zero drop shoes are also lightweight as there is generally less material to them as the extra cushioning usually used to build up the heel is not required, so this is advantageous on long, endurance trail runs.
Whether you opt for a more conventional heel to toe drop trail running shoe, or zero drop is entirely down to your preference, if you haven't used zero drop shoes before we suggest easing yourself into it as they can take some getting used to, however many will argue it's worth it. Regardless, there's no right or wrong and with increasing options in both styles you can be sure there's something out there for everyone.