Gladfield is a brand or company (maltster) that makes lots of different malts. Maris Otter is a variety of barley malted by several maltsters (different brands). The link below has good basic information on different base malts. I cut and pasted the section on Pale Malt, then there is Pale Ale Malt which as
@Golddiggie said is a little darker. Lots of malt brands, lots of different barley varieties and lots of different malts made from different varieties made by lots of different maltsters gets confusing.
From
Understanding Base Malt - Brew Your Own
Pale Malt
Pale Malt is the most common of the base malts used in beer. It is oftentimes called simply called “2-row” malt. This can be a little confusing to new brewers as basically all the malt they will be using is a type of 2-row malt. Just know that if a recipe calls for 2-row malt by name, they are referring to pale malt. Another name for the same type of malt might be the barley variety itself such as Maris Otter.
Pale malt is light in color and usually will be around 2–2.5 degrees Lovibond. It can be used to make basically any beer style and is highly modified so you will not have any trouble getting extract out of it. If you are not sure what base malt you should be using, start with pale malt. It works well in almost all situations. If you are looking to buy malt in bulk and store it yourself, this is definitely a must-have.