In the 21st Century, when we say Depression Glass, we normally mean mass produced and machine made tank glass from about 1920 to 1940, usually colored and of only fair quality. First, let's provide a bit of history. Hazel Marie Weatherman introduced us to the concept of "Depression Glass" books beginning with "A Guidebook to Colored Glassware of the 1920's and 1930's", self-published in 1969. In later books she changed her titling to "Colored Glassware of the Depression Era," but used companies making glass in the 1920's and 1930's as the boundaries. Those early books inspired interest in all those companies and helped create a wave of collecting. Others, like Debbie and Randy Coe, Gene and Cathy Florence, and Barbara and Jim Mauzy, have added significantly to the literature. While Ms. Weatherman included colored glass that was both cheaply mass produced and higher quality hand-blown or pressed glassware, distinctions developed. Mr. Florence is known for applying the words "Elegant Glass" to those products of a higher quality glass. This "better" glass was generally sold through department and jewelry stores, while the Depression Glass could be found in nickel and dime stores and often as premiums in boxes of food or soap or as incentives in stores, gas stations, or theaters. Kitchen and bath ware, including storage containers, spice and bath jars, juicers, mixing bowls, and so on were made by most of these companies. I would consider Depression Glass as everyday dishes for most families. Elegant Glass pieces were probably kept in the hutch for special occasions with the good china.
Depression Glass frequently carries the tag "Adam to Windsor", as these alphabetical bookends enveloped most commonly collected patterns. According to Wikipedia, more noteworthy companies included Anchor Hocking, Federal, Hazel-Atlas, Hocking, Indiana, Jeannette, Lancaster, McBeth-Evans, and L.E. Smith. Colors may have varied from batch to batch, if not within a single day. Little, if any, finishing resulted in pieces with distinct seams and sometimes indistinct patterns when brought from the molds. DG pieces may have straw marks (from severing molten glass), bubbles, or other imperfections, but always watch for distinct chips and cracks, which are different. Many of the collectible patterns continued well after 1940, some into the 1960s. Many have been reproduced, often by foreign countries (the Chinese made a lot of Cherry Blossom and Jadeite). Indiana Glass bought molds from other companies, reproducing The wise collector reads and often carries books.
Elegant Glass was generally made from higher quality formulae, involved hand pressing or blowing, and fire-finishing mold seams and edges. Many Elegant patterns include simple or intricate decoration (including acid etching, enameling, gold overlay, and such). Elegant patterns are frequently found on crystal as well as colored glass, unlike DG. Depression Glass patterns were a less expensive way to decorate glass that didn't involve hand etching that became so popular in the 1920s with the Elegant Glass. Elegant Companies generally began as Early American Pattern Glass (EAPG) companies, producing clear and colored dinnerware products beginning in the late 1800s up through about 1910. Cambridge, Duncan & Miller, Fenton, Fostoria, Heisey, Imperial, Morgantown, New Martinsville, and others began near or before 1900. A few patterns, like American, began in the 1910s and lasted until the 1980s or later. Plate-derived acid etchings began around 1910, but most of the popular Elegant etchings were made from the 1930s into the 1950s. It's these etchings that were mimicked in many DG patterns.
As if that weren't enough, some companies like Fry, Imperial, New Martinsville, Paden City, and a few others made glass that is identified in both Depression and Elegant Glass books. Oh, and some patterns appear in separate books as Depression and Elegant. These include Fenton Lincoln Inn, New Martinsville Moondrops and Radiance, and Paden City Peacock and Rose, and Westmoreland Della Robbia. Probably, although machine tank produced, the formulae were better and there was some additional finishing after removal from the mold.
Fenton, who made the first Carnival Glass in 1907, still made Elegant-labeled Hobnail into the 21st century. The artistry, desire, and business acumen of American Glass companies, no matter our somewhat arbitrary definitions, keeps our passion going for Depression, Elegant, or any American glass.