I suggest the following article (see the section "1.2 What is innovation?"):
FAGERBERG, Jan. Innovation: a guide to the literature. In: FAGERBERG, Jan; MOWERY, David C.; NELSON, Richard R. (edited by). The Oxford Handbook of Innovation. Oxford (UK): Oxford University Press, 2005. p. 1-26. ()
And the updated version of that text:
FAGERBERG, Jan. Innovation – a New Guide. Tik Working Papers on Innovation Studies, Oslo, n. 20131119, p. 1-45, 2013. ()
Simply put, innovation is the act of introducing something new (or reapplying old ideas in a new way). This said, definitions of innovation will inevitably be colored by the arena under discussion. See, for example, (i) Sparking Social Innovations, available at https://www.researchgate.net/publication/254583180_Sparking_Social_Innovations; (ii) Sparking Innovations in Management, available at https://www.researchgate.net/publication/254583234_Sparking_Innovations_in_Management; and (iii) Business Model Innovation, available at https://www.researchgate.net/publication/266477090_Business_Model_Innovation.
It can be interesting to see one text (mine) about inclusive innovation (in Spanish), a Working Paper: "Innovaciones sociales e inclusivas: límites y posibilidades para el desarrollo territorial en el contexto de la globalización" (it's in Researchgate or http://www.fee.rs.gov.br/tedes/innovaciones-sociales-e-inclusivas-limites-y-posibilidades-para-el-desarrollo-territorial-en-el-contexto-de-la-globalizacion/).