$\ce{PH3}$ and compounds derived from it by substituting one, two or three hydrogen atoms by hydrocarbyl groups $\ce{R3P}$. $\ce{RPH2}$, $\ce{R2PH}$ and $\ce{R3P}$ ($\ce{R} \neq \ce{H}$) are called primary, secondary and tertiary phosphines, respectively. A specific phosphine is preferably named as a substituted phosphane, e.g. $\ce{CH3PH2}$ methylphosphane.