Resheto (решето) is the Ukrainian word for a cross-hatched net design which resembles grating or a sieve.  Such netting is an ancient design which dates back to the Paleolithic Era (Old Stone Age, through 8000 BC), and symbolized the goddess of the sky.

According to traditional Ukrainian beliefs, the resheto has the talismanic of protection from evil spirits, and the sieve and the net are symbols of protection from evil spirits.  According to Selivachov, this explains why almost every design element contains crossed lines.

The resheto is not generally a separate design element, but fills in other motifs on a pysanka: circles, squares, rhombuses, triangles.  The resheto can sometimes be seen on pysanky from other parts of Ukraine, but is most beloved by those Ukrainians residing in the Carpathian region, particularly Hutsuls, Pokuttians and Bukovynian, who love to place gold and yellow resheto on their pysanky.  (Most regions outside of the Carpathians prefer to fill in shapes with stripes or solid colors instead of cross-hatching.)

These simple examples of resheto are from the Kyiv region (left and center) and the Boiko area of the Carpathians (right):

           

These more florid examples of resheto are from the ethnographic Hutsul areas of northern Bukovyna:

These are examples of Hutsul pysanky with resheto:

Examples of Pokuttian pysanky with a plethora of resheto, from the Easter market in Zabolotiv: