Several parts combine into one character.

域 is a phonetic-semantic compound: 土 (earth / land) + 或 (huò, "or / perhaps" — but originally a pictograph of a spear guarding a boundary). The etymological story is one of meaning-divergence: 或 originally meant "territory defended by weapons" — armed land. As 或 drifted toward the modern abstract meaning "perhaps / or," the territorial sense was lost, so the earth radical 土 was added to form a new character 域 specifically for "domain / territory / area." This is a textbook case where one character's semantic drift forces creation of a successor character to preserve the original meaning.

Korean reading "yeok." 區域 (guyeok, area / zone), 領域 (yeongyeok, domain / territory — used widely in academic and political discourse: "academic domain"), 地域 (jiyeok, region — central Korean political vocabulary: 지역감정 jiyeok-gamjeong "regional sentiment / regionalism," a major social topic), 異域 (iyeok, foreign land), 音域 (eumyeok, vocal range — music). Korean usage spans physical and abstract domains.

Mandarin yù, 4th tone. 域 (yù), 区域 (qūyù, area / zone), 领域 (lǐngyù, domain / field — same as Korean 영역), 地域 (dìyù — though modern Mandarin more often uses 地区 dìqū for region), 音域 (yīnyù, vocal range), 流域 (liúyù, river basin / drainage area), 网域 (wǎngyù, internet domain). The compound 域 + 名 = 域名 (yùmíng, "domain name") is the standard Mandarin term for internet domain names.

Japanese on-reading イキ (iki) — 地域 (chīki, region — top-frequency word in Japanese news, government, and community discourse: 地域社会 chīki shakai "local community"), 領域 (ryōiki, domain / sphere), 区域 (kuiki, zone / area), 異域 (iiki, foreign realm). 地域 is one of the most heavily used compounds in Japanese policy vocabulary, central to discussions of decentralization, local revitalization (地方創生 chihō-sōsei), and aging-society programs.

Memory aid: 或 originally meant defended territory but drifted to mean "or"; the earth radical (土) was added to keep the territorial sense alive in a new character = domain.