A line graph, not necessarily on a grid, that shows the general shape of the relationship between two variables.
It will not have any points plotted and although the axes should be labelled they may not be scaled.
The top graph shows a good sketch of the general trend shown by whatever data was looked at; it is a nice smooth curve. Unfortunately the person creating the graph forgot to label the axes! Whoops - this will no doubt reduce their mark overall.
The bottom graph shows a well-labelled pair of graph axes and the points look great! However, although a pattern is implied by the crosses, there is no line!
No line on a sketch graph, no way can you get full marks.