滑行 (huá xíng) means 'to slide or coast' — it emphasizes smooth, continuous movement over a surface, often with momentum (e.g., a plane taxiing, a car sliding on ice). It is broader than 滑 (huá), which is more general ('to slip, slide, or glide') and also means 'slippery' as an adjective. Unlike 滑雪 (huá xuě, 'to ski') or 滑冰 (huá bīng, 'to ice skate'), 滑行 does not specify a sport or equipment.