Historically, the term "dataset" originated in the mainframe field. A data set (or dataset) is a collection of data, usually presented in tabular form. Each column represents a variable. Each row corresponds to a member of the data set. It lists values for each of the variables. The data set may comprise data for one or more members, corresponding to the number of rows.
A dataset in RDF represents a body of knowledge, technically a collection of RDF statements which can be interpreted as RDF graph. RDF datasets is formally defined in the specification of the SPARQL query language. Dataset is a collection of RDF graphs against which the query is evaluated. SPARQL datasets consists of one default graph and multiple named graphs, i.e. RDF graphs identified by URIs.
In LOD and LDSR dataset is used in the sense of collection of data (e.g. a database dump) represented in RDF.