..."The habitat of a species, or population of a species, is the sum of the abiotic and biotic factors of the environment, whether natural or modified, which are essential to the life and reproduction of the species within its natural geographic range (adapted from Council of Europe 1989 )."
This definition is broadly similar to, but more specific than, that given in the MA (2003 ) which is:
"the environmental attributes required by a particular species (its ecological niche)"
It also conforms to the general definition given by the Convention on Biodiversity (1992) which is:
"The place or type of site where an organism or population naturally occurs (Secretariat of the Convention on Biological Diversity (2001)" .
A species’ habitat may change during different stages of life, for example in many freshwater insects which have an aquatic growth stage followed by a terrestrial reproductive stage. ... ( Harrington, R. et al., 2010 )

References:

• Council of Europe (1989) Standing Committee of the Berne Convention Resolution No. 1, 1989 on the provisions relating to the conservation of habitats. Council of Europe, Strasbourg

• Harrington, R. et al., 2010: Ecosystem services and biodiversity conservation: concepts and a glossary. Biodivers Conserv, DOI 10.1007/s10531-010-9834-9, Springer

• MA (Millennium Ecosystem Assessment) (2003) Ecosystems and human well-being. Island Press, Washington

• Secretariat of the Convention on Biological Diversity (2001) Handbook of the Convention on Biological Diversity. Earthscan Publications, London