Nomenclature - Lanthanoids vs Lanthanides (and Actinides vs Actinoids)
According to p 52, Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005 (‘Red Book’):


  The ending ‘ide’
  normally indicates a negative ion, and therefore lanthanoid and actinoid are preferred to
  lanthanide and actinide.


In practice this is almost never followed, and consequently both terms are (for all intents and purposes) interchangeable, unless the context demands a differentiation.