Left Anarchism is a broad, general term usually used to group together a few different forms of anarchism, including both organizational anarcho-communism (platformism) and anti-organizational anarcho-communism (insurrectionism), anarcho-syndicalism as well as some forms of anti-capitalist market anarchism, green anarchism and individualist anarchism.
These forms of anarchism are radically left-wing in that they aim to eliminate class/economic hierarchy, and other forms of oppression or inequality such as racism, patriarchy, cis-sexism, shadeism, etcetera. Thus they have some common traits with socialist and communist ideas, but are nonetheless forms of anarchism in that they oppose hierarchy and the state.
Red Anarchism, Social Anarchism, and Left Libertarianism are all fairly similar terms.
Some have argued that these terms are redundant, as all forms of anarchism are "left wing", and the term serves only to exclude "right wing anarchisms" such as "anarcho-capitalism" and "national anarchism", which really should not be counted as anarchism at all.
On the other hand, there are also many anarchists, including many green anarchists, primitivists, insurrectionists, individualists and egoists, identify as "post-left", rejecting the left-right political spectrum and criticizing many aspects of the traditional left, while still opposing capitalism and all other forms of domination.