The difference can begin to be seen in the origins of the words. Congress is based on an ancient Latin word meaning "a coming together," which is precisely what happens in a congress representatives from all the parts of a nation coming together to discuss matters of state. Parliament, however, has its roots in a French word meaning "To talk," and there certainly is a great deal of talking going on in any parliament.
In fact, this simple linguistic difference leads one to the chief difference in the election process. A congress is based upon primary elections in which the general populace selects their candidates more based upon their personalities and individual plans for office, while in a parliament, the delegates are chosen to run by their own political parties based almost entirely on their willingness to follow party standards. While party certainly comes into play in any congress, the individual really does mean more in elections to that body.
And it is that sense of individuality that leads to the second main difference between the two. In a parliamentary government, the Prime Minister and his cabinet (The leaders of the nation) are chosen from the majority party in the country's parliament. Thus, if the members of that party begin voting against their party's ideals in the body, the entire government can come apart, forcing an election of a new Prime Minister. With this in place, many parties very carefully restrict the freedoms of their delegates to ensure the safety of their Prime Ministers. In a congress, however, the executive branch