What is the difference between an expansion and an incarnation of the Lord?

Answer by HH Bhakti Vikāsa Swami: 

These are English terms. Or Russian, or whatever. The word incarnation is often used by Śrīla Prabhupāda to refer to avatāra – one who descends into this world. All living beings are expansions of the Supreme Lord. They’re in two divisions – svāṁśa and vibhinnāṁśa. Svāṁśa means that they are the parts, but they are the own part, or what you might call an expansion. And they may or may not descend into this material world. Vibhinnāṁśa means the jīvas. So, we are separated parts of the Supreme Lord.