Some may assume that the tomcat is a male cat that can be seen on the street but in the world of Java, this is much different. These are known to be Java servlet application servers. JBoss is considered to be the more advanced version because it can offer so much more.
It can be confusing to know the difference between the two but a lot of people refer to TomCat as an application server probably because it is being used more for different applications as compared to JBoss but JBoss can be more compatible with the different Java EE application stack. TomCat is known to have more limitations as compared to JBoss.