Jim is right, the photos show an early version of "fighting tops" fitted to war vessels. These appear to be on an Elizabethan-era galleon of northern European origin. However, no matter where the ship was knocked together, they were a development of the "top," a platform which originated with the development of multi-sectional masts. These platforms usually had gratings for sailors to walk and work running rigging.
Technically, the "mast" (fore, main, mizzen, jigger, etc.) is the section that buries at the keel and goes through the decks to end just above the course. This uppermost reach of the mast was the top until rigs grew taller and more sections were added above the mast. Sailors being somewhat stuck in their ways still called the top of the mast "the top." It was also known as the "head" of the mast but we'll go there later.
The next section up was the top mast and, then came the upper top mast. It was easy enough to attach shrouds (standing rigging from the port and starboard sides) to the mast. It became necessary to put a special structure for wide enough support the upper shrouds at the top. Being built at the old mast top, these were dubbed as "tops" on commercial ships and "fighting tops" ob men o'war. The significant difference was more space on warships for marines to place musket fire on the decks of enemy vessels.
Admiral Lord Nelson was killed by an enemy musket ball in this manner. Look up the story.
Above the mast came the topmast and then the upper topmast. Weight that far aloft was a problem, so on most ships crosstrees served in the place of platforms. If there was an origin of the crow's nest as we know them, it was at the crosstrees. They were high for visibility and gave full view of the horizon. Many whaling and fishing vessels had iron hoops installed to hold the man on lookout firmly in place against the heave of the ship.
The topmast was usually the uppermost vertical spar. It was generally crowed with a piece of wood intended to keep water from coming into the vertical grain of the mast. This was the "truck," and the word remains in the nautical lexicon to describe the upper reach of the mast (nowadays, usually a single piece metal tube).
White lights indicating a steamship (showing 225 deg of arc) are sometimes called "mashead lights" because of their location partway up the mast. However, with the demise of "tops," their placement is somewhat arbitrary with the broad limits of the Rules of the Road.
Anyway working from the highest position to the keel the key parts of a muti-section mast are:
2. Upper Topmast
3. Crosstrees (or sometimes "trestle trees")
5. Top or fighting top
7. Bury (section of mast inside hull)
8. Heel Lower end of mast keyed into keel.
A silver coin was traditionally placed under the foremast heel, gold under the main mast, and copper under the mizzen.
Oh, yes, a "ship" by definition is a three-masted, square-rigged vessel. Titanic with only two masts and no yards was a schooner.
-- David G. Brown