A quite simple word. Englacial means "inside a glacier", or "formerly within a glacier". 'Englacial debris' refer to rocks that were carried along within a glacier. Till deposits, moraines, eskers, and kames are all englacial formations.
Not to be confused with interglacial, a period of warmth between to glacial periods. It may, however, very well be confused with subglacial, meaning "underneath a glacier". Subglacial is used in reference to lakes and volcanoes beneath the glacier, while englacial is more often used to refer to the debris carried within the ice, but there is a large amount of crossover in usage. Moraines in particular may be referred to as either englacial or subglacial.