【冷や酒 (ひやざけ hiyazake)】cold sake
冷や酒 (hiyazake) is technically sake served at room temperature, but it is commonly called "cold sake" since back when there were no refrigerators, sake was served either warm or 冷や (hiya) — "cold" at room temperature. Both 冷や酒 (hiyazake) and 冷酒 (reishu) may be considered "cold sake," but there is a difference. With advances in technology and brewing styles, today Japanese sake can be served and enjoyed in various degrees of "cold" and "hot."
冷酒 (reishu) is in general "chilled" sake but there are different degrees with a name for each level.
雪冷え (yukibie) 5℃ — 雪 (yuki); snow
花冷え (hanabie) 10℃ — 花冷え (hanabie); chilly spring weather
涼冷え (suzubie) 15℃ — 涼しい (suzushii); cool
冷や (hiya) 20℃
日向燗 (hinatakan) 30℃ — 日向 (hinata); sunny
人肌燗 (hitohadakan) 35℃ — 人肌 (hitohada); body temperature
ぬる燗 (nurukan) 40℃
上燗 (jyōkan) 45℃
熱燗 (atsukan) 50℃
飛び切り燗 (tobikirikan) 55℃ — 飛び切り (tobikiri); extremely, super
(Source via here)
Like wine, every sake has a unique character. Certain 日本酒 (nihonshu) are brewed to be enjoyed 冷や (room temperature) or slightly chilled, while others are better warmed.