spine; line of the back; backbone line
Refers to the vertical line along the back or spine, especially in posture expressions such as 背筋を伸ばす.
I sat in the chair with my back straight.
Hearing the scary story sent a chill down my spine.
back seam; seam down the back of clothing
Clothing and sewing use: the seam or line running down the back of a garment.
The seam down the back of the jacket is slightly crooked.
Her back is perfectly straight, and she has a beautiful standing posture.
This dress has a zipper along the back seam.
I sat down in the chair with my back muscles engaged.
縫い目 is the general term for any seam or stitch line, while 背筋 in this sense specifically names the seam running down the back of a garment.
姿勢 is the general word for posture or bearing, whereas 背筋 specifically points to the straightness of the back, as in 背筋を伸ばす.
背中 means the whole back of the body, while 背筋 refers narrowly to the vertical line or seam running down it.
腹筋 refers to the abdominal muscles (front of the torso), while 背筋 refers to the back muscles, and the two are easy to mix up since both are 〜筋 body-part terms used in fitness talk.
striped field mouse
Standard kanji spelling with the reading せすじ.
Mixed kanji-kana spelling that makes the すじ part explicit; useful when emphasizing the せすじ reading.
A compound of 背, meaning the back, and 筋, meaning a line, strand, or streak; the spelling reflects the idea of the line running along the back.