参照物 is a physics and everyday term meaning 'reference object' or 'frame of reference' — the thing you compare something else to in order to judge its position, movement, or change. In daily life, you use it when describing relative motion (e.g., 'the tree is the reference point') or when making comparisons ('compared to last year's model'). It's a compound of 参照 (to refer to) and 物 (object).