frame rail

Short definition from Wiktionary

Noun

1. 1
   Each of the two main longitudinal structural members of a body‑on‑frame vehicle, running parallel front to rear and supporting the chassis, to which cross‑members, suspension, drivetrain, and body are attached.
2. 2
   A horizontal structural member of a furniture frame, typically joining the legs or vertical posts, providing support and rigidity; commonly found in tables, chairs, cabinets, and beds.