Leaky parts of an old tent, often

• Sewer lines?
• Sutures
• Lines of juncture
• Baseball features
• Where garments often split
• Sites of some bursting
• Clothing lines
• Some stockings have them
• Clothing joints

Wiktionary Word definitions in Wiktionary
n. (plural of seam English) vb. (en-third-person singular of: seam )