Dome

The dome, dome section, head section or head dome, (PROSE: The Dalek Generation, Prisoner of the Daleks) was the top part or "head" of a Dalek's casing, atop the grating section, upon which the eyepiece and luminosity discharger was mounted. It was connected to the rest of the casing via a docking clamp. (TV: Resurrection of the Daleks)

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)

Opening
By releasing the docking clamp which connected the dome to their upper grating section, a Dalek could open up, exposing their mutant form underneath. (TV: Resurrection of the Daleks)

While operating a vacant Dalek casing within the Moroks' Space Museum, the First Doctor opened up the dome to peek his head out of the casing. (TV: The Space Museum)

Aboard a Prison Station, two Daleks sent by the Supreme Dalek released their docking clamps, ostensibly so that Kiston could extract samples of Dalek tissue for Davros' research into the Movellan virus. In reality, the device used by Kiston, once administered to the mutant Daleks, conditioned them to obey Davros. (TV: Resurrection of the Daleks)

As a distinguishing feature
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)

As Emperor of the Imperial Daleks, Davros was housed in a casing with a larger, spherical dome which replaced the weapons platform. Sporting Imperial luminosity dischargers and a black-outlined silver hexagon in place of the eyepiece, Davros could chose to open up dome's top half to reveal himself. (TV: Remembrance of the Daleks)

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

Uniquely, the Black Dalek overseer had exceptionally short luminosity dischargers in comparison to even pre-Time War Daleks, as well as an eyepiece with a red lens. (AUDIO: Planet of the Ogrons)

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)

The dark green, robotic Proto-Daleks, which were constructed by the British and Germans as part of the Dalek Project during the First World War, had distinct domes; the British Proto-Daleks' luminosity dischargers were shaped like smaller glass hemispheres, while the domes of German Proto-Daleks had a point at the top, mirroring the helmets worn by contemporary German troops, with luminosity dischargers that were narrow, orange, cylindrical and larger than any true Dalek. (COMIC: The Dalek Project)

Individual cases
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) after being attacked by the Could've Been Kings. (PROSE: Dalek Caan)

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 "Quasimodo Dalek", which was reconstructed by unfamiliar humans, had a dome with a gunstick in the place of the eyepiece, two of which were then fitted to its weapons platform, while sense globes replaced its luminosity dischargers. (COMIC: The Dalek Project)

The dome of a red Supreme Dalek was seen at UNIT's Black Archive in the 2010s. (TV: The Day of the Doctor)

Other references
The Dalek Troopers led by Gustave Lytton wore helmets resembling Dalek domes. (TV: Resurrection of the Daleks)

The human interface of the Dalek battle computer wore a similar black dome with eyepiece. (TV: Remembrance of the Daleks)

Behind the scenes

 * 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.
 * James Johnson's Time War-era Reconnaissance Dalek, which was featured on the cover of Gallifrey: War Room 1: Allegiance, was a bronze Dalek distinguished by a red dome.