收附等温线（英语：sorption isotherm，又称为吸附等温线）描述了一种物质于某一常温下在某种表面（通常在界面上）上的收附平衡。它表明了束缚于表面（吸附质）上该种物质的量是该种物质在气相或溶液中浓度的函数。吸附等温线常被作为经验模型来使用，也就是说经验模型并不去说明收附的潜在机理或实测的可变因素。这些收附等温线是依靠回归分析而得到的。最常用的等温线有：线性等温线、弗罗因德利希等温线、朗缪尔等温线与BET模型。

Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the absorbate) is dissolved by or permeates a liquid or solid (the absorbent), respectively. Adsorption is a surface-based process while absorption involves the whole volume of the material. The term sorption encompasses both processes, while desorption is the reverse of it. Adsorption is a surface phenomenon.