You can picture an armature as the hard thing inside that holds a soft or moving thing together. A lump of clay cannot stand up by itself, so the maker puts a wire frame inside it first. A 3D character is only a surface, so the puts a chain of bones inside it. A motor needs one part that carries the wire and turns, so the wire is wound onto a core. In each case the armature is not the thing you look at. It is the part underneath that lets the thing hold its shape or do its work.
From the word’s history
Wiktionary gives the source as Middle French armature, from Latin armatura, meaning armour, and notes that armor and armure are doublets of it. Armour is a hard shell built to hold and protect a body, and that picture of a firm supporting structure is what stayed in the word after the fighting sense faded.
依 Wiktionary 的說明，armature 來自中古法文 armature，再往上是拉丁文 armātūra（盔甲），和 armor、armure 同源。盔甲是一副撐住身體、保護身體的硬殼。打仗的意思後來淡掉了，但「一副硬的支撐結構」這個畫面留了下來，正好對上今天的雕塑骨架和馬達鐵芯。
Wiktionary, "armature"
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