じゃあ

じゃあ is a casual contraction of では. One of the most commonly used words in spoken Japanese for transitions, conclusions, and farewells.

FORMALITY SCALE:

• では: formal (speeches, business)
• それでは: polite (meetings, formal conversation)
• じゃあ: casual (everyday conversation)
• じゃ: even more casual

MAIN FUNCTIONS:
1. Transition: じゃあ、始(はじ)めましょう (Well then, let's begin)
2. Consequence: じゃあ、傘(かさ)を持(も)っていこう (Then let's take an umbrella)
3. Farewell: じゃあね / じゃあ、また (See you! / See you later)

NOTE:
Very frequently used at the start of sentences. Almost never used in formal writing — use では or それでは instead.