noun
ready-made goods; off-the-shelf item
Refers to mass-produced, pre-made products as opposed to custom-made or made-to-order items. Common in commercial and manufacturing contexts.
このスーツは既製品ですが、サイズがぴったりです。
This suit is ready-made, but it fits perfectly.
既製品の家具は注文品より安い。
Ready-made furniture is cheaper than custom-made.
レディメイド is a loanword from English 'ready-made', often used in fashion and design contexts, while 既製品 is the native Japanese term used more broadly.
Compound of 既 (already) + 製 (manufactured) + 品 (goods). The word transparently means 'already-manufactured goods'.