There are several different kinds of hot peppers. One is the Jalapeno. It is only hot if you eat the seeds of them. The green chili peppers include the Jalapenos, but there are other peppers in this group. The other green chili peppers include cayenne peppers and Anaheim. All of these peppers are considered hot. They have a thin flesh and seeds that make it hot. Even though these peppers are hot, they range in heat on a scale.
Some are hotter than others. The green chili pepper, Jalapeno is considered to be the hottest pepper in this group. Several of the other green chili peppers are long and grow many inches long, but Jalapeno peppers are caught small in size.
There are two categories of peppers: spicy and sweet. Jalapenos and green chilis are both in spicy category, meaning they are botanically the same. This is where the similarities end. Green chilis are referred to as "Anaheim" peppers and are less spicy than the Jalapeno and are used to make green chili and canned chilies. Jalapeno peppers are known to be spicy and used in small quantities to add heat.
To give you an idea of the difference in spicy flavor, Jalapenos are rated a 5 out of 10 in heat, where green chilies rank around 2 or 3. Typically, Anaheim peppers are roasted before use and jalapenos are diced or minced and used fresh. Jalapeno peppers are also popular to be pickled.