What is the meaning of a deca-core processor?

A deca core literally means just that. Deca, ten, 10, weapon X, Roman numeral ten.

Deaccore means a processor which has 10 physical Cpu cores on board a single piece of silicon.

The source where you most likely would have heard it is in mobile space where some 1.5 years ago, mediatek announced a decacore processor named “Helios X20” (later to be succeeded by, X25 and X30)

It has 10 cores, 8 cortex A53, divided in 2 clusters of 4. And 2 high performance A72 cores.

Although, it's not a first processor to feature that number of cores. PC market long has Xeons packing greater than 10 cores.and the biggest consumer cpu’s made by Intel, called extreme edition have been deca cores for some time now. Current one is i7 6950x.

The biggest Xeon intel has is 22 cores Xeon E5 2699 V5

The biggest cores packing offers from AMD would be Naples server core, likely called Ryzen 4700, featuring 32 cores in a single package. Itll likely launch in 2nd half of this year.