The term “Soft Maple” does not refer to any specific species of maple, but rather, it’s a broad term which includes several different species of maple. The term “Soft Maple” is merely used to differentiate these species from Hard Maple.
Depending on where you live, different species might be sold as Soft Maple. Some of the most common are Red Maple and Silver Maple.
Each of these maples have their own characteristics regarding strength, hardness, weight, etc., but overall, they are not as hard nor as strong as Hard Maple.