In strict definition "lane splitting", "lane sharing", & "filtering up" all have different specific meanings although often confused for each other.

Most FRAP laws as written require "lane sharing" with the cyclist in the right edge of the lane and the car in the left edge of the lane when the lanes are not too narrow (usually they are) for that to be done safely.

"Lane Sharing" is two (or more) vehicles sharing a lane side-by-side while both are moving down the road, not necessarily at the same speed. The best example of such is two motorcycles sharing a lane one riding in the right tire track and one riding in the left tire track. I personally am very careful about sharing lanes with cars in this kind of side-by-side arrangement and rarely do it, usually with me on the left side of the lane when I'm preparing for a left hand turn and the cars behind me want to continue going straight. I personally would much rather ride on the shoulder edge to the right of the white fog line then try to share a lane side-by-side with cars with me in the right edge of the lane but still inside of it to the left of the white fog line. Even on wide 14+ foot wide traffic lanes (what few there are in my area) I'm very uncomfortable with that position and would much rather be "IN" or "OUT" of the main traffic lane.

"Lane Splitting" is riding on the line between two lanes of moving traffic both going the same direction and is practiced almost exclusively by narrow two wheel vehicles such as bicycles and motorcycles. If on 4-lane street with two lanes of full size vehicles going in each direction you decide to ride your bike on the dashed white line between the fast and slow lanes on your side of the street then you are "lane splitting". Riding on the white fog line on the far right of the roadway is not "lane splitting" because there is not a lane of moving traffic on both sides of you, just one one side. To "split" is to go in-between. In strict definition lane splitting is riding on the line between two lanes of moving traffic with moving traffic on both sides of you and you riding right on the line in-between them. When I'm riding FRAP instead of taking the lane I personally will "lane split" on the white line between the straight through traffic lane and the right hand turn lane when I intend to continue going straight through the intersection but heavy traffic is moving at too high of a speed for me to "take the lane" unless I have to do so and there is a good safe shoulder edge to ride on except for when there is a right hand turn lane and I don't want to get clobbered by right hand turning traffic because I was trying to continue straight through while to the right of that right turn only lane. That is about the only time I personally with "lane split" because for that particular situation it works out to be the best option both for me and also to "be nice" to other road users.

"Filtering Up" in specific definition refers to working your way through stopped or barely moving heavy vehicle traffic. If the heavy vehicle traffic is moving its either "lane sharing" or "lane splitting" or "riding on the shoulder edge outside of the main lanes" but when they aren't moving and are stopped such as when they are waiting for a red light or in a traffic jamb then its all refereed to as "filtering up" as soon as they are also moving it is no longer filtering up. Filtering up when done with proper caution can be one the least dangerous of the three because if all the cars are boxing each other in they can't suddenly turn into you when your at their side. The one exception being the lead vehicles in the lanes stopped at the light, those front place vehicles can and will move as soon as they can and you should be extra careful when filtering up on the right with that last lead vehicle and I personally when filtering up on the right will usually stop just behind the lead vehicles rear bumper and in plain sight of the vehicle immediately behind the lead vehicle so I don't get right hooked by that lead vehicle if the driver decides to turn right either when the light turns green or suddenly make a right on red. You also have to watch out for doors opening or people sticking stuff out of their windows as well but when filtering up at least the cars themselves aren't moving and are all boxing each other in which gives you a noticeable safety advantage provided you don't push it too far and get careless.