Question

help: can someone please explain to me in simple terms what the eutectic point is?

Answer 1

A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition. This composition is known as the eutectic composition and the temperature is known as the eutectic temperature. On a phase diagram the intersection of the eutectic temperature and the eutectic composition gives the eutectic point.

Not all binary alloys have a eutectic point; for example, in the silver-gold system the melt temperature (liquidus) and freeze temperature (solidus) both increase monotonically as the mix changes from pure silver to pure gold
http://www.myhomefoundry.com/casting_info/eutectic-point.pdf

Answer 2

A lay example is the use of ethylene glycol in your radiator. Water freezes at 32F and ethylene Glycol at -10F. But in combination the two freeze at still lower temps and at a specific combination this reached a minimum - the eutectic point. In the case of Ethylene Glycol and water it is about 70% Ethylene glycol resulting in a freezing point of -60F.