Cero

Cero is the strongest single shared attacked by upper-level Hollows

Description
is a form of attack used by menos, arrancar and vizards. It consists of firing a blast of concentrated energy at the target. While most are fired from the mouth, some are capable of firing from their hands, fingers and such.

The power of the cero is dependant on the strength of the user (I.E. the stronger the user the stronger the attack), and there are those that have come up with their own variation.

Cero Doble
Cero doble, Spanish for "double zero" is a variation performed by Neliel Tu Oderschvank, by swallowing her opponents cero and returning it back to the user along with her own cero. This attack was first seeing used against Nnoitra Jiruga.

While in her child form, Nel is only able to return the cero fired by her opponent as seen used against Dordonii Alessandro Del Socacchio.

Cero Sincrético
is a variation performed by Dondochakka Bilstin and Pesche Guatiche. This attack was first seen being used against Szayel Aporro Granz.

Beautiful Charlotte Cuulhorn's Final Holy Wonderful Pretty Super Magnum Sexy Sexy Glamourous Cero
This variation is performed by Charlotte Cuulhorn. Despite it's long name and the shape of heart it is just an ordinary cero as noted by Yumichika Ayasegawa.

Gran Rey Cero
is an Espada-exclusive Cero. It is performed by mixing an Arrancars own blood with the cero. The result is a cero with a much greater attack power and speed, as well as a change of color unique to the Espada. This attack was first used by Grimmjow Jeagerjaques in order to incite Ichigo Kurosaki in to dawning his mask.

Others
While most cero are red, Ichigo's Hollow form's cero is tri-focused and pink, Ulquiorra Schiffer's is green, and Grimmjow Jeagerjaques's is blue.