Facebook (NASDAQ:FB) stock was pummeled last week, falling about 19% after the company reported its second-quarter results. Lower-than-expected revenue and management's forecast for a rapid deceleration in its year-over-year top-line growth for the remainder of the year sent shares sharply downward.

As investors consider the implications of Facebook's results, here are a handful of quotes from its earnings call to help gain a better overall picture of the social network. Important insights from the second-quarter earnings call include a look at the company's new metric, management's forecast for a narrowing gross margin, and more.

The address sign with a thumbs-up icon outside the main entrance to Facebook HQ.

Image source: Facebook.

1. About Facebook's new metric

Facebook introduced a new metric during the quarter: familywide audience. At 2.5 billion users, Facebook's familywide audience count is higher than any of the monthly active user (MAU) figures the company boasts for any of its platforms, including its core Facebook platform, which has 2.23 billion MAUs.

The metric is defined as the number of people across the world using one of its applications in a given month. Unlike other MAU metrics, this measures the number of people -- not accounts -- using its services on a monthly basis and it consolidates these metrics for all of Facebook's social platforms.

Facebook CFO David Wehner explained the metric:

This is our best estimate of our de-duplicated audience across Facebook, Instagram, Messenger, and WhatsApp. We believe this number better reflects the size of our community and the fact that many people are using more than one of these services.

For some context on the impact of only counting monthly active individuals instead of monthly active accounts, Wehner noted that approximately 10% of the MAUs reported for Facebook have multiple accounts. "The family audience metric only counts a single user in these instances," Wehner explained.

2. Instagram is a big growth driver

Recently surpassing 1 billion monthly active users, Instagram is now integral to Facebook's overall results -- especially since Facebook has spent far more resources monetizing Instagram than it has any of its other non-Facebook platforms.

Though Facebook doesn't specify how much advertising revenue is coming from Instagram, Facebook COO Sheryl Sandberg suggests it's material:

The ads have expanded quite nicely to Instagram. And Instagram represents a very healthy part of the growth and we expect that to continue as well.

3. What's next after Instagram?

When asked how management ranks its platforms in terms of business opportunities over the next couple of years, Sandberg first unsurprisingly noted that Instagram is the biggest near-term opportunity beyond the core Facebook platform.

But what's Facebook's next-best business opportunity over the next few years? That would be Messenger, Sandberg said.

We are furthest ahead in Messenger, but it's still very early days. We're quite happy with the consumer engagement with 1.3 billion monthly actives on the platform. And we continue to see a lot of organic connections between businesses and consumers on the messaging platform. We now have over 8 billion messages sent between people and businesses per month, which includes automated messages. We're being very slow and deliberate with monetization; it's still in early days.

After Messenger, Sandberg said WhatsApp is the next frontier. "We are very focused there on the user experience, but we're also focused, even earlier stages [than Instagram], on growing our business ecosystem," Sandberg said.

4. Facebook's operating margin is headed lower

Another factor that likely contributed to Facebook stock's sell-off besides a forecast for year-over-year revenue growth rates to decelerate by high single-digit percentages sequentially in both Q3 and Q4 was Wehner's commentary on the company's gross margin trajectory:

Over the next several years, we would anticipate that our operating margins will trend toward the mid 30s on a percentage basis.

This will be caused by operating expense growth that exceeds revenue growth, Wehner said. This trend was already true in Q2, with revenue rising 42% year over year and operating expenses jumping 50%. This caused Facebook's operating margin to decline from 46% in Q1 to 44% in Q2.