The phrase "cobblestone streets" refers to roads or pathways that are made up of small, rounded stones. These stones are typically laid in a pattern and compacted together to create a smooth surface for walking or driving on. Cobblestone streets were commonly used during the 19th century as they provided better drainage than traditional paved surfaces, but have since been largely replaced by modern pavement materials. Today, cobblestone streets are often seen as charming and historic features in older neighborhoods or tourist areas.