What is Candlestick Chart?

Legal Definition
A candlestick chart (also called Japanese candlestick chart) is a style of financial chart used to describe price movements of a security, derivative, or currency. Each "candlestick" typically shows one day; so for example a one-month chart may show the 20 trading days as 20 "candlesticks".

It is like a combination of line-chart and a bar-chart: each bar represents all four important pieces of information for that day: the open, the close, the high and the low. Being densely packed with information, they tend to represent trading patterns over short periods of time, often a few days or a few trading sessions.

Candlestick charts are most often used in technical analysis of equity and currency price patterns. They appear superficially similar to box plots, but are unrelated.
-- Wikipedia
Legal Definition
A tool used to understand present prices and predicting future price actions. By the understanding of this, the trader knows when best to buy and sell, thereby making more profits in his transactions or A chart that indicates the trading range for the day as well as the opening and closing price. If the open price is higher than the close price, the rectangle between the open and close price is shaded. If the close price is higher than the open price, that area of the chart is not shaded.