Altar

Definition
A designated space, typically a table or flat surface, in which a practitioner|witch keeps tools, has (if any) religious or sacred items or offerings to give, and space to work within.

Can also be described as a space that helps a practitioner|witch focus on their practice, a ritual, ceremony, etc.

Satanic Alters
"An altar is simply a structure, usually elevated, which serves as a sacred space and upon which one may conduct ritual work, offer libations to one's deities or establish a shrine to a deity or person amongst many other purposes." Source
 * LaVeyan Satanists: "Do not acknowledge nor honour an external deity such as Satan, an altar would serve the purpose of enabling them to carry out their symbolic ritual acts by "appearing" to be a traditional "Satanic" altar.  One may find upon such an altar an array of typically "Satanic" items - the Baphometic inverse pentagram, a ritual blade, a chalice of red wine, etc.  These items serve as aids to LaVeyan psychodrama, yet do not typically possess any function outside of what may be considered "props"".
 * Theistic Satanism (Luciferians) and Demonolatry: "the altar often functions as an intermediary space which unites both the physical and the unseen, great care is taken to keep the space and all items occupying that space clean and consecrated".

Wiccan Alters
Altars tend to be of great importance to Wiccan practitioners|witches. Some Wiccans would describe it as a symbolic manifestation of the practitioner's inner self, in which you can create a focal point to the divine deities you favor.