Santosha (skt. संतोष saṃtoṣa) literally means "contentment, satisfaction".
It can simple be called Cheerfulness..
Winter is a time when the weather is very harsh. It can make us feel gloomy, dull and sometimes sad. The sun has a tremendous influence on us. So during winter, when visibility is less, it is time to invoke the "Inner Sun" - enthusiasm and cheerfulness.
Cheerfulness helps in developing contentment and peace. It's the doorway to the Self. Cheerfulness has innumerable benefits, such as releasing the feel-good-hormones (Serotonin, Oxytocin, Dopamine, Endorphins). Even amidst stressful situations we can keep up our cheerfulness and this will bring in all those neuro-chemicals. This is why Patanjali included it as one of the Niyamas (Personal Practices).
DO! Do something everyday (for 10 minutes) which makes you happy. You can sing a song, draw a picture, massage your feet, juggle with 3 balls, write in your gratitude journal, or even collect some leaves and flowers and make a flower vase.
MEDITATE! Set the timer for 5 minutes. Sit in an easy chair, close your eyes and smile. Remember to keep your phone in airplane mode during this time.
SMILE! Smile while commuting. Smile in your workplace. Smile even when there anxious moments.
PLAY! Play with children and pets.