Ethereum is the largest decentralised application platform in cryptocurrency. You might be wondering what a decentralised application platform is. In a nutshell, it is a blockchain on which applications can be built. You could think of it as an operating system like IOS or Android, upon which application like Candy Crush are builtYes, Ethereum is the second largest cryptocurrency out there.
However, things move very quickly in technology. For those who are old enough to remember, Internet Explorer used to have complete dominance in the web browser market. Now its nowhere to be seen. The point is that technology evolves and just because a cryptocurrency (like Ethereum) is big today, doesnt mean that something better will come along and make it obsolete.