Support
Support is a price area where buyers have already halted a decline at least once, and where demand may win out again.
You draw support by connecting lows where price bounced. The more often the area has been tested and the sharper the bounce, the more closely traders watch it. It is better to think of a zone than a line accurate to the pip.
Support often forms on round numbers (1.0800 on EUR/USD, $2,300 on gold, 18,000 on the DAX), old highs or weekly lows.
When support breaks decisively, it often turns into resistance: trapped buyers sell to get out at break-even when price comes back to the area. This is the principle of role reversal.