Steganography refers to the hiding of any form of secret data - text, image, audio or video within another non secret message or data. In Image Steganography the data was transmitted by hiding it within an Image.
In this method the LSB bits of pixels of non secret image was repalced by the bits of secret messsage. It is done so because the LSB contains minimum information and the MSB contains the maximum information, therefore by replacing the LSB bits of pixels of non secret image with MSB bits secret message, results in transmitting the most of the information of secret message.