Dome

The dome of Dalek Sec. (TV: Doomsday)

The dome was the top part or "head" of a Dalek's casing, upon which the eyepiece and luminosity discharger was mounted. At GeoComTex, the Ninth Doctor instructed security personnel to aim for the "Metaltron's" dome, specifically the eyepiece. (TV: Dalek) Similarily, the Fifth Doctor instructed British Army soldiers to aim for the eyepiece, "the stalk at the top of the dome". (TV: Resurrection of the Daleks)

As a distinguishing feature

Dalek 1. (COMIC: The Only Good Dalek)

Typically, the domes of most Daleks matched the majority of their casings. (TV: The Daleks et al.)

Across Dalek history, the Emperor's Personal Guard were distinguished by their black domes. (TV: The Evil of the Daleks, The Parting of the Ways) A minority of bronze-type Daleks aboard the Dalek Emperor's flagship following the Last Great Time War had black base units with golden sense globes in addition to a black dome similar to that of the Emperor's Personal Guard. (TV: The Parting of the Ways)

As well as a black dome, the Dalek saucer commander was distinguished by alternating black-and-silver panels on the base unit. (TV: The Dalek Invasion of Earth)

During the Last Great Time War, members of the Dalek Scientific Division were distinguished by their blue domes. (AUDIO: A Thing of Guile)

During the 41st century war between the Space Security Service and the New Dalek Paradigm, captured Daleks were taken aboard Station 7 and distinguished by numbered tags which were placed on the dome next to the eyepiece. (COMIC: The Only Good Dalek)

As a result of his incursion to retrieve Davros from the time-locked Last Great Time War, Dalek Caan lost his dome as well as a substantial portion of his casing. (TV: The Stolen Earth)

A pair of "Ironside" Daleks deployed by the British Army against the Luftwaffe had covers placed over their luminosity dischargers. These covers were removed by the time they deserted and were subsequently destroyed by the New Dalek Paradigm. (TV: Victory of the Daleks)

The "Dalek Patrol Ship" sets released in 2014 by Character Options included an exclusive 3.75-inch bronze "Dalek pilot" figurine bearing a black dome and alternating black "skirt" panels identical to the colour scheme of the Dalek saucer commander.
In Dalek Hack, the player has the option to change the colour of a Dalek's casing which is divided into three sections, including the dome attached to the grating section.