后备 (hòubèi) refers to backup personnel or resources kept in reserve, such as a backup team or a reserve plan. Contrast with 备用 (bèiyòng), which describes spare physical items (e.g., 备用钥匙 spare key), and 备份 (bèifèn), which is specifically a data backup. 后备 often appears in compound words like 后备箱 (trunk) and 后备力量 (reserve forces).