I think he meant the difference between high and low pressure markers (judging by his opening line: "anyone tell me the differecne between high and low pressure markers??")
. High pressure markers operate at a higher pressure (in psi), resulting in a harder bolt to ball impact. Low pressure markers run at lower pressures, but sometimes at the risk of efficiency since low pressure = high volume. However, they're less likely to break balls (lower bolt to ball impact), have lower kick and are supposedly more stable. High pressure is generally associated with cheaper, blowback markers like the Spyder and Tippmann lines (and their clones) that use blowback air to help re-cock the marker. Low pressure is typically associated with higher end markers that incorporate a low pressure recocking system.