Flickr Gallery is not what you'd normally expect. It's limited in a way that you can curate up to 50 photos on Flickr, taken by anyone but you. Formerly they were limited to 18 pictures. Flickr's idea behind a mandatory limit is that it helps people only choose the best of the best when they curate. After all, the space on the walls at an exhibition is limited too. It's a great way to show your appreciation towards certain themes and ideas and create a small gallery. There are various hand-picked galleries on Flickr that you can explore. Add their curator to Justified Image Grid then you can pick the gallery you wish to show. Are you looking for Flickr Albums instead?
Displaying a curated Flickr Gallery
Check it out on Flickr as well: Winter. Note the special (foreign) characters in the grid below.
It allows you to add 3rd-party images to a gallery but not those that you own. In this sense, they are different from Albums. Being limited by how many photos a Flickr Gallery can hold ensures a more interesting, better quality selection.