In a strict sense, the silyl group is $\ce{H3Si\bond{–}}$.
A name commonly applied to hydrocarbyl derivatives of the silyl group $\ce{R3Si\bond{–}}$.
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1366 [Terms] [Paper]