noun
reflected wave; echo
Technical term used in physics, acoustics, and related fields for a wave that has bounced back from a surface or boundary.
レーダーは反射波を検出して物体の位置を特定する。
Radar detects reflected waves to determine the position of objects.
超音波検査では、体内からの反射波を画像
In ultrasound examination, reflected waves from inside the body are turned into an image.
エコー is a common loanword for 'echo' in everyday contexts, whereas 反射波 is a more technical term.
Compound of 反射 (reflection) + 波 (wave). The exact historical derivation is uncertain, but the components are straightforward.