Definition of pure bhakti:
jnana karmadi anavritam
["The cultivation of activities that are meant exclusively for the pleasure of Sri Krsna, or in other words the uninterrupted flow of service to Sri Krsna, performed through all endeavours of the body, mind and speech, and through the expression of various spiritual sentiments (bhavas), which is not covered by jnana (knowledge aimed at impersonal liberation) and karma (reward-seeking activity), and which is devoid of all desires other than the aspiration to bring happiness to Sri Krsna, is called uttama-bhakti, pure devotional service."
(Sri Bhakti-rasamrta-sindhu 1.1.11)]
In brief, the meaning of the verse is this: Pure bhakti is the continuous, unbroken cultivation of all activities of the body, mind, words, and spiritual feelings which are meant exclusively for the benefit of Sri Krsna, which are completely free from all other desires, and which is not covered by karma (fruitive activities), jnana (knowledge to get liberation), yoga, and other things.