Just like its name sounds, it is essentially a mermaid / lion. The "Mer" part of its name (meaning "sea") is a reference to the fact that Singapore is a port city and earns its livelihood from maritime trade. The "lion" part refers to Singapore's nickname given by the Malay king who thought he saw a lion when he first visited the island and named it "Lion City" in ancient Singapore history.
Stopping by the Merlion in Singapore is kind of like visiting the Eiffel Tower when in Paris or the Cristo Redentor when in Rio de Janeiro. You just HAVE TO see it!
It may not be as big in size, but it is as uniquely Singapore as those other monuments are to their respective countries.
Merlion park may be a bit of a tourist trap with crowds of people at times for this reason. But it has an excellent view and is a great spot to take pictures. Best of all it's FREE!