alkyl groups

https://doi.org/10.1351/goldbook.A00228
Univalent groups derived from alkanes by removal of a hydrogen atom from any carbon atom –CnH2n+1. The groups derived by removal of a hydrogen atom from a terminal carbon atom of unbranched alkanes form a subclass of normal alkyl (n-alkyl) groups H(CH2)n. The groups RCH2, R2CH (RH), and R3C (RH) are primary, secondary and tertiary alkyl groups, respectively.
See also: cycloalkyl groups, hydrocarbyl groups
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1314 (https://doi.org/10.1351/pac199567081307)