A partial collar strike is when the collar die (edge die) does not fully engage the edge of the planchet. The collar die's purpose is the engage the rim of the coplanchet so it doesn't spread out from the striking pressure (broad strike) and to impart edge reeding to coins to coins like U.S. dimes, half dollars and quarters.
If a planchet is jammed and tilted in the coining chamber or the collar itself is damaged (broken) then it strikes the wrong area of the edge, and this results in what looks like a dual rim, part of the coin to be spread out or both. Also it can look like railroad tracks if the coin has edge reeding.
Most offten a partial collar strike will look like a line running around half the coin's rim but the more severe the more anomolies can occur and some will display half the reeding missing.
People call dimes, quarters, half dollars and large dollars "Railroad" rims when they're partial collar strike and some of he edge reeding is struck out of place. It's not uncommon to find this with modern dimes and unless dramatic it doesn't add much if any value, and that includes the quarters and half dollars, but the larger the denomination the more valuable this will get.