What is the difference in terms of strategy, between wanting to grow or expand its idea?

Mr.Emmanuel pointed it very cleary, nothing to add. 

Thanks for invitation....I endorse answers given by Mr.Emmanuel Wamweta

GROWTH

Michael Porter's Model: overall cost leadership (lowest cost producer relative competitors, increase firm's profitability, affordable proces), differenciation (adding to customer percieved value, continuous innovatiojs & inventions, uniqueness) And focus strategy (segmenation, focus on segements & niches, specialisation on segments & niches).

EXPANSION

Gluek's Approach: Expansion- a firm adds to its markets & fuctions, expends to surive a volatile environment, to provide variety & assortments, sign of good performance & need to re-invest.

Thanx for the invitation, its always a pleasure contriubuting